v3.25.2
Shareholder Report
12 Months Ended
Jul. 31, 2025
USD ($)
Holding
Shareholder Report [Line Items]  
Document Type N-CSR
Amendment Flag false
Registrant Name BlackRock Funds
Entity Central Index Key 0000844779
Entity Investment Company Type N-1A
Document Period End Date Jul. 31, 2025
C000129315  
Shareholder Report [Line Items]  
Fund Name BlackRock Short Obligations Fund
Class Name Institutional Shares
Trading Symbol BISOX
Annual or Semi-Annual Statement [Text Block] This annual shareholder report contains important information about BlackRock Short Obligations Fund (the “Fund”) for the period of August 1, 2024 to July 31, 2025.
Shareholder Report Annual or Semi-Annual Annual Shareholder Report
Additional Information [Text Block] You can find additional information about the Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 441-7762.
Material Fund Change Notice [Text Block]

Additional Information Website blackrock.com/fundreports
Expenses [Text Block]

What were the Fund costs for the last year?

(based on a hypothetical $10,000 investment)

Class name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Institutional Shares
$29
0.29%
Expenses Paid, Amount $ 29
Expense Ratio, Percent 0.29%
Factors Affecting Performance [Text Block]

How did the Fund perform last year?

  • For the reporting period ended July 31, 2025, the Fund's Institutional Shares returned 4.77%.

  • For the same period, the Fund’s benchmark, the Bloomberg U.S. Aggregate Bond Index, returned 3.38% and the ICE BofA 6-Month U.S. Treasury Bill Index, returned 4.60%.

What contributed to performance?

The Fund’s duration positioning contributed to absolute performance (duration is a measure of interest rate sensitivity). Asset allocation—namely, positions in U.S. Treasuries, commercial paper, and investment-grade corporate bonds—also helped results. The Fund’s cash position had no material impact on performance.

What detracted from performance?

At a time of positive returns for the broader fixed-income markets, no aspect of the Fund’s positioning was a significant detractor.

Performance Past Does Not Indicate Future [Text] Past performance is not an indication of future results.
Line Graph [Table Text Block]

Fund performance

Cumulative performance: August 1, 2015 through July 31, 2025

Initial Investment of $10,000 

Growth of 10K Chart
Institutional Shares
Bloomberg U.S. Aggregate Bond Index
ICE BofA 6-Month U.S. Treasury Bill Index
Aug 15
$10,005
$9,986
$10,001
Sep 15
$10,010
$10,053
$10,011
Oct 15
$10,015
$10,055
$10,008
Nov 15
$10,020
$10,028
$10,007
Dec 15
$10,016
$9,996
$10,012
Jan 16
$10,023
$10,133
$10,020
Feb 16
$10,030
$10,205
$10,024
Mar 16
$10,058
$10,299
$10,033
Apr 16
$10,065
$10,338
$10,040
May 16
$10,073
$10,341
$10,041
Jun 16
$10,080
$10,527
$10,053
Jul 16
$10,098
$10,594
$10,056
Aug 16
$10,106
$10,581
$10,057
Sep 16
$10,115
$10,575
$10,066
Oct 16
$10,124
$10,494
$10,072
Nov 16
$10,133
$10,246
$10,074
Dec 16
$10,146
$10,261
$10,079
Jan 17
$10,155
$10,281
$10,086
Feb 17
$10,175
$10,350
$10,092
Mar 17
$10,176
$10,344
$10,092
Apr 17
$10,187
$10,424
$10,100
May 17
$10,207
$10,504
$10,106
Jun 17
$10,218
$10,494
$10,115
Jul 17
$10,229
$10,539
$10,126
Aug 17
$10,240
$10,634
$10,140
Sep 17
$10,251
$10,583
$10,147
Oct 17
$10,253
$10,589
$10,156
Nov 17
$10,265
$10,575
$10,164
Dec 17
$10,270
$10,624
$10,175
Jan 18
$10,274
$10,502
$10,187
Feb 18
$10,287
$10,402
$10,193
Mar 18
$10,292
$10,469
$10,207
Apr 18
$10,308
$10,391
$10,222
May 18
$10,337
$10,465
$10,240
Jun 18
$10,346
$10,452
$10,256
Jul 18
$10,366
$10,455
$10,274
Aug 18
$10,397
$10,522
$10,293
Sep 18
$10,417
$10,454
$10,307
Oct 18
$10,428
$10,372
$10,327
Nov 18
$10,450
$10,433
$10,347
Dec 18
$10,466
$10,625
$10,371
Jan 19
$10,512
$10,738
$10,394
Feb 19
$10,534
$10,732
$10,413
Mar 19
$10,570
$10,938
$10,438
Apr 19
$10,583
$10,941
$10,460
May 19
$10,617
$11,135
$10,485
Jun 19
$10,650
$11,275
$10,514
Jul 19
$10,673
$11,299
$10,534
Aug 19
$10,705
$11,592
$10,562
Sep 19
$10,725
$11,531
$10,580
Oct 19
$10,745
$11,565
$10,607
Nov 19
$10,763
$11,559
$10,619
Dec 19
$10,781
$11,551
$10,637
Jan 20
$10,810
$11,774
$10,653
Feb 20
$10,826
$11,986
$10,681
Mar 20
$10,734
$11,915
$10,736
Apr 20
$10,834
$12,127
$10,736
May 20
$10,878
$12,183
$10,734
Jun 20
$10,897
$12,260
$10,736
Jul 20
$10,916
$12,443
$10,740
Aug 20
$10,922
$12,343
$10,741
Sep 20
$10,917
$12,336
$10,743
Oct 20
$10,922
$12,281
$10,744
Nov 20
$10,926
$12,401
$10,746
Dec 20
$10,930
$12,418
$10,748
Jan 21
$10,933
$12,329
$10,749
Feb 21
$10,936
$12,151
$10,751
Mar 21
$10,928
$12,000
$10,753
Apr 21
$10,931
$12,094
$10,754
May 21
$10,944
$12,134
$10,755
Jun 21
$10,936
$12,219
$10,754
Jul 21
$10,938
$12,356
$10,755
Aug 21
$10,941
$12,332
$10,756
Sep 21
$10,943
$12,225
$10,756
Oct 21
$10,934
$12,222
$10,756
Nov 21
$10,926
$12,258
$10,756
Dec 21
$10,928
$12,227
$10,757
Jan 22
$10,909
$11,964
$10,752
Feb 22
$10,901
$11,830
$10,751
Mar 22
$10,861
$11,501
$10,747
Apr 22
$10,854
$11,065
$10,751
May 22
$10,872
$11,136
$10,763
Jun 22
$10,848
$10,962
$10,756
Jul 22
$10,882
$11,229
$10,766
Aug 22
$10,899
$10,912
$10,781
Sep 22
$10,884
$10,441
$10,798
Oct 22
$10,907
$10,305
$10,816
Nov 22
$10,955
$10,684
$10,855
Dec 22
$10,997
$10,636
$10,901
Jan 23
$11,064
$10,963
$10,938
Feb 23
$11,085
$10,680
$10,970
Mar 23
$11,122
$10,951
$11,028
Apr 23
$11,180
$11,018
$11,066
May 23
$11,220
$10,898
$11,093
Jun 23
$11,248
$10,859
$11,146
Jul 23
$11,313
$10,851
$11,192
Aug 23
$11,368
$10,782
$11,243
Sep 23
$11,401
$10,508
$11,293
Oct 23
$11,459
$10,342
$11,344
Nov 23
$11,529
$10,810
$11,403
Dec 23
$11,602
$11,224
$11,462
Jan 24
$11,652
$11,193
$11,512
Feb 24
$11,687
$11,035
$11,552
Mar 24
$11,737
$11,137
$11,604
Apr 24
$11,785
$10,856
$11,650
May 24
$11,835
$11,040
$11,705
Jun 24
$11,896
$11,144
$11,755
Jul 24
$11,969
$11,405
$11,817
Aug 24
$12,031
$11,569
$11,879
Sep 24
$12,092
$11,724
$11,940
Oct 24
$12,128
$11,433
$11,979
Nov 24
$12,162
$11,554
$12,023
Dec 24
$12,210
$11,365
$12,075
Jan 25
$12,269
$11,425
$12,118
Feb 25
$12,311
$11,676
$12,156
Mar 25
$12,358
$11,681
$12,198
Apr 25
$12,403
$11,727
$12,240
May 25
$12,449
$11,643
$12,277
Jun 25
$12,494
$11,822
$12,321
Jul 25
$12,541
$11,790
$12,361

See “Average annual total returns” for additional information on fund performance.

Average Annual Return [Table Text Block]

Average annual total returns

Average Annual Total Returns
1 Year
5 Years
10 Years
Institutional Shares ........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
4.77%
2.81%
2.29%
Bloomberg U.S. Aggregate Bond Index........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.38
(1.07)
1.66
ICE BofA 6-Month U.S. Treasury Bill Index........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
4.60
2.85
2.14
No Deduction of Taxes [Text Block] Performance results do not reflect the deduction of taxes that a shareholder would pay on fund distributions or on the redemption or sale of fund shares.
Performance Table Market Index Changed [Text Block]  
Material Change Description [Text Block]  
Updated Performance Information Location [Text Block] Visit blackrock.com for more recent performance information. 
AssetsNet $ 1,113,134,413
Holdings Count | Holding 247
Advisory Fees Paid, Amount $ 1,523,024
InvestmentCompanyPortfolioTurnover 59.00%
Additional Fund Statistics [Text Block]

Key Fund statistics

Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
$1,113,134,413
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
247
Net Investment Advisory Fees........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
$1,523,024
Portfolio Turnover Rate........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
59%
Holdings [Text Block]

Portfolio composition

Maturity allocation

Asset Type
Percent of Net Assets
Corporate Bonds........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
42.0%
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.0
Asset-Backed Securities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
1.7
Foreign Agency Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
0.7
Municipal Bonds........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
0.4
Short-Term Securities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
52.5
Liabilities in Excess of Other Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
(0.3)
Percent of Net Assets
1-7 days........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
6.0%
8-14 days........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.6
15-30 days........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
1.4
31-60 days........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
10.2
61-90 days........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
5.4
91-120 days........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
12.0
121-150 days........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
2.4
>150 days........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
59.0
C000198747  
Shareholder Report [Line Items]  
Fund Name BlackRock Short Obligations Fund
Class Name Investor A Shares
Trading Symbol BASOX
Annual or Semi-Annual Statement [Text Block] This annual shareholder report contains important information about BlackRock Short Obligations Fund (the “Fund”) for the period of August 1, 2024 to July 31, 2025.
Shareholder Report Annual or Semi-Annual Annual Shareholder Report
Additional Information [Text Block] You can find additional information about the Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 441-7762.
Material Fund Change Notice [Text Block]

Additional Information Website blackrock.com/fundreports
Expenses [Text Block]

What were the Fund costs for the last year?

(based on a hypothetical $10,000 investment)

Class name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Investor A Shares
$51
0.50%
Expenses Paid, Amount $ 51
Expense Ratio, Percent 0.50%
Factors Affecting Performance [Text Block]

How did the Fund perform last year?

  • For the reporting period ended July 31, 2025, the Fund's Investor A Shares returned 4.65%.

  • For the same period, the Fund’s benchmark, the Bloomberg U.S. Aggregate Bond Index, returned 3.38% and the ICE BofA 6-Month U.S. Treasury Bill Index, returned 4.60%.

What contributed to performance?

The Fund’s duration positioning contributed to absolute performance (duration is a measure of interest rate sensitivity). Asset allocation—namely, positions in U.S. Treasuries, commercial paper, and investment-grade corporate bonds—also helped results. The Fund’s cash position had no material impact on performance.

What detracted from performance?

At a time of positive returns for the broader fixed-income markets, no aspect of the Fund’s positioning was a significant detractor.

Performance Past Does Not Indicate Future [Text] Past performance is not an indication of future results.
Line Graph [Table Text Block]

Fund performance

Cumulative performance: August 1, 2015 through July 31, 2025

Initial Investment of $10,000 

Growth of 10K Chart
Investor A Shares
Bloomberg U.S. Aggregate Bond Index
ICE BofA 6-Month U.S. Treasury Bill Index
Aug 15
$9,992
$9,986
$10,001
Sep 15
$10,004
$10,053
$10,011
Oct 15
$10,006
$10,055
$10,008
Nov 15
$10,009
$10,028
$10,007
Dec 15
$10,002
$9,996
$10,012
Jan 16
$10,006
$10,133
$10,020
Feb 16
$10,010
$10,205
$10,024
Mar 16
$10,036
$10,299
$10,033
Apr 16
$10,040
$10,338
$10,040
May 16
$10,046
$10,341
$10,041
Jun 16
$10,060
$10,527
$10,053
Jul 16
$10,065
$10,594
$10,056
Aug 16
$10,071
$10,581
$10,057
Sep 16
$10,077
$10,575
$10,066
Oct 16
$10,093
$10,494
$10,072
Nov 16
$10,100
$10,246
$10,074
Dec 16
$10,100
$10,261
$10,079
Jan 17
$10,107
$10,281
$10,086
Feb 17
$10,124
$10,350
$10,092
Mar 17
$10,132
$10,344
$10,092
Apr 17
$10,140
$10,424
$10,100
May 17
$10,149
$10,504
$10,106
Jun 17
$10,157
$10,494
$10,115
Jul 17
$10,166
$10,539
$10,126
Aug 17
$10,175
$10,634
$10,140
Sep 17
$10,184
$10,583
$10,147
Oct 17
$10,193
$10,589
$10,156
Nov 17
$10,203
$10,575
$10,164
Dec 17
$10,206
$10,624
$10,175
Jan 18
$10,207
$10,502
$10,187
Feb 18
$10,208
$10,402
$10,193
Mar 18
$10,221
$10,469
$10,207
Apr 18
$10,235
$10,391
$10,222
May 18
$10,252
$10,465
$10,240
Jun 18
$10,269
$10,452
$10,256
Jul 18
$10,286
$10,455
$10,274
Aug 18
$10,305
$10,522
$10,293
Sep 18
$10,322
$10,454
$10,307
Oct 18
$10,342
$10,372
$10,327
Nov 18
$10,351
$10,433
$10,347
Dec 18
$10,376
$10,625
$10,371
Jan 19
$10,409
$10,738
$10,394
Feb 19
$10,429
$10,732
$10,413
Mar 19
$10,462
$10,938
$10,438
Apr 19
$10,484
$10,941
$10,460
May 19
$10,516
$11,135
$10,485
Jun 19
$10,547
$11,275
$10,514
Jul 19
$10,557
$11,299
$10,534
Aug 19
$10,587
$11,592
$10,562
Sep 19
$10,605
$11,531
$10,580
Oct 19
$10,634
$11,565
$10,607
Nov 19
$10,640
$11,559
$10,619
Dec 19
$10,656
$11,551
$10,637
Jan 20
$10,683
$11,774
$10,653
Feb 20
$10,708
$11,986
$10,681
Mar 20
$10,615
$11,915
$10,736
Apr 20
$10,712
$12,127
$10,736
May 20
$10,754
$12,183
$10,734
Jun 20
$10,771
$12,260
$10,736
Jul 20
$10,777
$12,443
$10,740
Aug 20
$10,781
$12,343
$10,741
Sep 20
$10,784
$12,336
$10,743
Oct 20
$10,787
$12,281
$10,744
Nov 20
$10,778
$12,401
$10,746
Dec 20
$10,780
$12,418
$10,748
Jan 21
$10,781
$12,329
$10,749
Feb 21
$10,781
$12,151
$10,751
Mar 21
$10,782
$12,000
$10,753
Apr 21
$10,783
$12,094
$10,754
May 21
$10,783
$12,134
$10,755
Jun 21
$10,784
$12,219
$10,754
Jul 21
$10,784
$12,356
$10,755
Aug 21
$10,784
$12,332
$10,756
Sep 21
$10,773
$12,225
$10,756
Oct 21
$10,763
$12,222
$10,756
Nov 21
$10,763
$12,258
$10,756
Dec 21
$10,753
$12,227
$10,757
Jan 22
$10,742
$11,964
$10,752
Feb 22
$10,721
$11,830
$10,751
Mar 22
$10,690
$11,501
$10,747
Apr 22
$10,682
$11,065
$10,751
May 22
$10,697
$11,136
$10,763
Jun 22
$10,672
$10,962
$10,756
Jul 22
$10,692
$11,229
$10,766
Aug 22
$10,707
$10,912
$10,781
Sep 22
$10,701
$10,441
$10,798
Oct 22
$10,711
$10,305
$10,816
Nov 22
$10,756
$10,684
$10,855
Dec 22
$10,806
$10,636
$10,901
Jan 23
$10,859
$10,963
$10,938
Feb 23
$10,878
$10,680
$10,970
Mar 23
$10,923
$10,951
$11,028
Apr 23
$10,967
$11,018
$11,066
May 23
$11,004
$10,898
$11,093
Jun 23
$11,041
$10,859
$11,146
Jul 23
$11,091
$10,851
$11,192
Aug 23
$11,143
$10,782
$11,243
Sep 23
$11,184
$10,508
$11,293
Oct 23
$11,228
$10,342
$11,344
Nov 23
$11,294
$10,810
$11,403
Dec 23
$11,364
$11,224
$11,462
Jan 24
$11,422
$11,193
$11,512
Feb 24
$11,454
$11,035
$11,552
Mar 24
$11,501
$11,137
$11,604
Apr 24
$11,534
$10,856
$11,650
May 24
$11,593
$11,040
$11,705
Jun 24
$11,638
$11,144
$11,755
Jul 24
$11,708
$11,405
$11,817
Aug 24
$11,766
$11,569
$11,879
Sep 24
$11,823
$11,724
$11,940
Oct 24
$11,857
$11,433
$11,979
Nov 24
$11,900
$11,554
$12,023
Dec 24
$11,944
$11,365
$12,075
Jan 25
$11,987
$11,425
$12,118
Feb 25
$12,026
$11,676
$12,156
Mar 25
$12,082
$11,681
$12,198
Apr 25
$12,112
$11,727
$12,240
May 25
$12,155
$11,643
$12,277
Jun 25
$12,209
$11,822
$12,321
Jul 25
$12,253
$11,790
$12,361

See “Average annual total returns” for additional information on fund performance.

Average Annual Return [Table Text Block]

Average annual total returns

Average Annual Total Returns
1 Year
5 Years
10 Years
Investor A Shares ........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
4.65%
2.60%
2.05%
Bloomberg U.S. Aggregate Bond Index........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.38
(1.07)
1.66
ICE BofA 6-Month U.S. Treasury Bill Index........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
4.60
2.85
2.14
No Deduction of Taxes [Text Block] Performance results do not reflect the deduction of taxes that a shareholder would pay on fund distributions or on the redemption or sale of fund shares.
Performance Table Market Index Changed [Text Block]  
Material Change Description [Text Block]  
Updated Performance Information Location [Text Block] Visit blackrock.com for more recent performance information. 
AssetsNet $ 1,113,134,413
Holdings Count | Holding 247
Advisory Fees Paid, Amount $ 1,523,024
InvestmentCompanyPortfolioTurnover 59.00%
Additional Fund Statistics [Text Block]

Key Fund statistics

Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
$1,113,134,413
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
247
Net Investment Advisory Fees........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
$1,523,024
Portfolio Turnover Rate........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
59%
Holdings [Text Block]

Portfolio composition

Maturity allocation

Asset Type
Percent of Net Assets
Corporate Bonds........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
42.0%
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.0
Asset-Backed Securities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
1.7
Foreign Agency Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
0.7
Municipal Bonds........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
0.4
Short-Term Securities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
52.5
Liabilities in Excess of Other Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
(0.3)
Percent of Net Assets
1-7 days........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
6.0%
8-14 days........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.6
15-30 days........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
1.4
31-60 days........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
10.2
61-90 days........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
5.4
91-120 days........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
12.0
121-150 days........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
2.4
>150 days........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
59.0
C000119004  
Shareholder Report [Line Items]  
Fund Name BlackRock Short Obligations Fund
Class Name Class K Shares
Trading Symbol BBSOX
Annual or Semi-Annual Statement [Text Block] This annual shareholder report contains important information about BlackRock Short Obligations Fund (the “Fund”) for the period of August 1, 2024 to July 31, 2025.
Shareholder Report Annual or Semi-Annual Annual Shareholder Report
Additional Information [Text Block] You can find additional information about the Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 441-7762.
Material Fund Change Notice [Text Block]

Additional Information Website blackrock.com/fundreports
Expenses [Text Block]

What were the Fund costs for the last year?

(based on a hypothetical $10,000 investment)

Class name
Costs of a $10,000 investment
Costs paid as a percentage of a $10,000 investment
Class K Shares
$21
0.20%
Expenses Paid, Amount $ 21
Expense Ratio, Percent 0.20%
Factors Affecting Performance [Text Block]

How did the Fund perform last year?

  • For the reporting period ended July 31, 2025, the Fund's Class K Shares returned 4.76%.

  • For the same period, the Fund’s benchmark, the Bloomberg U.S. Aggregate Bond Index, returned 3.38% and the ICE BofA 6-Month U.S. Treasury Bill Index, returned 4.60%.

What contributed to performance?

The Fund’s duration positioning contributed to absolute performance (duration is a measure of interest rate sensitivity). Asset allocation—namely, positions in U.S. Treasuries, commercial paper, and investment-grade corporate bonds—also helped results. The Fund’s cash position had no material impact on performance.

What detracted from performance?

At a time of positive returns for the broader fixed-income markets, no aspect of the Fund’s positioning was a significant detractor.

Performance Past Does Not Indicate Future [Text] Past performance is not an indication of future results.
Line Graph [Table Text Block]

Fund performance

Cumulative performance: August 1, 2015 through July 31, 2025

Initial Investment of $10,000 

Growth of 10K Chart
Class K Shares
Bloomberg U.S. Aggregate Bond Index
ICE BofA 6-Month U.S. Treasury Bill Index
Aug 15
$9,995
$9,986
$10,001
Sep 15
$10,010
$10,053
$10,011
Oct 15
$10,015
$10,055
$10,008
Nov 15
$10,021
$10,028
$10,007
Dec 15
$10,017
$9,996
$10,012
Jan 16
$10,024
$10,133
$10,020
Feb 16
$10,031
$10,205
$10,024
Mar 16
$10,059
$10,299
$10,033
Apr 16
$10,067
$10,338
$10,040
May 16
$10,075
$10,341
$10,041
Jun 16
$10,093
$10,527
$10,053
Jul 16
$10,100
$10,594
$10,056
Aug 16
$10,110
$10,581
$10,057
Sep 16
$10,118
$10,575
$10,066
Oct 16
$10,137
$10,494
$10,072
Nov 16
$10,147
$10,246
$10,074
Dec 16
$10,151
$10,261
$10,079
Jan 17
$10,160
$10,281
$10,086
Feb 17
$10,180
$10,350
$10,092
Mar 17
$10,192
$10,344
$10,092
Apr 17
$10,203
$10,424
$10,100
May 17
$10,214
$10,504
$10,106
Jun 17
$10,225
$10,494
$10,115
Jul 17
$10,237
$10,539
$10,126
Aug 17
$10,249
$10,634
$10,140
Sep 17
$10,261
$10,583
$10,147
Oct 17
$10,274
$10,589
$10,156
Nov 17
$10,287
$10,575
$10,164
Dec 17
$10,293
$10,624
$10,175
Jan 18
$10,297
$10,502
$10,187
Feb 18
$10,301
$10,402
$10,193
Mar 18
$10,317
$10,469
$10,207
Apr 18
$10,334
$10,391
$10,222
May 18
$10,363
$10,465
$10,240
Jun 18
$10,373
$10,452
$10,256
Jul 18
$10,393
$10,455
$10,274
Aug 18
$10,424
$10,522
$10,293
Sep 18
$10,445
$10,454
$10,307
Oct 18
$10,456
$10,372
$10,327
Nov 18
$10,479
$10,433
$10,347
Dec 18
$10,495
$10,625
$10,371
Jan 19
$10,542
$10,738
$10,394
Feb 19
$10,565
$10,732
$10,413
Mar 19
$10,590
$10,938
$10,438
Apr 19
$10,615
$10,941
$10,460
May 19
$10,650
$11,135
$10,485
Jun 19
$10,684
$11,275
$10,514
Jul 19
$10,707
$11,299
$10,534
Aug 19
$10,729
$11,592
$10,562
Sep 19
$10,750
$11,531
$10,580
Oct 19
$10,782
$11,565
$10,607
Nov 19
$10,790
$11,559
$10,619
Dec 19
$10,809
$11,551
$10,637
Jan 20
$10,839
$11,774
$10,653
Feb 20
$10,867
$11,986
$10,681
Mar 20
$10,775
$11,915
$10,736
Apr 20
$10,877
$12,127
$10,736
May 20
$10,921
$12,183
$10,734
Jun 20
$10,942
$12,260
$10,736
Jul 20
$10,951
$12,443
$10,740
Aug 20
$10,957
$12,343
$10,741
Sep 20
$10,963
$12,336
$10,743
Oct 20
$10,968
$12,281
$10,744
Nov 20
$10,973
$12,401
$10,746
Dec 20
$10,977
$12,418
$10,748
Jan 21
$10,981
$12,329
$10,749
Feb 21
$10,974
$12,151
$10,751
Mar 21
$10,977
$12,000
$10,753
Apr 21
$10,981
$12,094
$10,754
May 21
$10,984
$12,134
$10,755
Jun 21
$10,987
$12,219
$10,754
Jul 21
$10,990
$12,356
$10,755
Aug 21
$10,993
$12,332
$10,756
Sep 21
$10,985
$12,225
$10,756
Oct 21
$10,988
$12,222
$10,756
Nov 21
$10,980
$12,258
$10,756
Dec 21
$10,972
$12,227
$10,757
Jan 22
$10,964
$11,964
$10,752
Feb 22
$10,945
$11,830
$10,751
Mar 22
$10,917
$11,501
$10,747
Apr 22
$10,910
$11,065
$10,751
May 22
$10,929
$11,136
$10,763
Jun 22
$10,906
$10,962
$10,756
Jul 22
$10,930
$11,229
$10,766
Aug 22
$10,947
$10,912
$10,781
Sep 22
$10,944
$10,441
$10,798
Oct 22
$10,957
$10,305
$10,816
Nov 22
$11,006
$10,684
$10,855
Dec 22
$11,060
$10,636
$10,901
Jan 23
$11,116
$10,963
$10,938
Feb 23
$11,138
$10,680
$10,970
Mar 23
$11,187
$10,951
$11,028
Apr 23
$11,235
$11,018
$11,066
May 23
$11,276
$10,898
$11,093
Jun 23
$11,316
$10,859
$11,146
Jul 23
$11,371
$10,851
$11,192
Aug 23
$11,427
$10,782
$11,243
Sep 23
$11,472
$10,508
$11,293
Oct 23
$11,520
$10,342
$11,344
Nov 23
$11,591
$10,810
$11,403
Dec 23
$11,664
$11,224
$11,462
Jan 24
$11,715
$11,193
$11,512
Feb 24
$11,751
$11,035
$11,552
Mar 24
$11,802
$11,137
$11,604
Apr 24
$11,852
$10,856
$11,650
May 24
$11,914
$11,040
$11,705
Jun 24
$11,964
$11,144
$11,755
Jul 24
$12,039
$11,405
$11,817
Aug 24
$12,102
$11,569
$11,879
Sep 24
$12,164
$11,724
$11,940
Oct 24
$12,201
$11,433
$11,979
Nov 24
$12,248
$11,554
$12,023
Dec 24
$12,285
$11,365
$12,075
Jan 25
$12,345
$11,425
$12,118
Feb 25
$12,388
$11,676
$12,156
Mar 25
$12,436
$11,681
$12,198
Apr 25
$12,482
$11,727
$12,240
May 25
$12,530
$11,643
$12,277
Jun 25
$12,589
$11,822
$12,321
Jul 25
$12,612
$11,790
$12,361

See “Average annual total returns” for additional information on fund performance.

Average Annual Return [Table Text Block]

Average annual total returns

Average Annual Total Returns
1 Year
5 Years
10 Years
Class K Shares ........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
4.76%
2.86%
2.35%
Bloomberg U.S. Aggregate Bond Index........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.38
(1.07)
1.66
ICE BofA 6-Month U.S. Treasury Bill Index........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
4.60
2.85
2.14
No Deduction of Taxes [Text Block] Performance results do not reflect the deduction of taxes that a shareholder would pay on fund distributions or on the redemption or sale of fund shares.
Performance Table Market Index Changed [Text Block]  
Material Change Description [Text Block]  
Updated Performance Information Location [Text Block] Visit blackrock.com for more recent performance information. 
AssetsNet $ 1,113,134,413
Holdings Count | Holding 247
Advisory Fees Paid, Amount $ 1,523,024
InvestmentCompanyPortfolioTurnover 59.00%
Additional Fund Statistics [Text Block]

Key Fund statistics

Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
$1,113,134,413
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
247
Net Investment Advisory Fees........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
$1,523,024
Portfolio Turnover Rate........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
59%
Holdings [Text Block]

Portfolio composition

Maturity allocation

Asset Type
Percent of Net Assets
Corporate Bonds........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
42.0%
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.0
Asset-Backed Securities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
1.7
Foreign Agency Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
0.7
Municipal Bonds........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
0.4
Short-Term Securities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
52.5
Liabilities in Excess of Other Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
(0.3)
Percent of Net Assets
1-7 days........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
6.0%
8-14 days........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
3.6
15-30 days........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
1.4
31-60 days........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
10.2
61-90 days........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
5.4
91-120 days........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
12.0
121-150 days........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
2.4
>150 days........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
59.0