v3.26.1
Shareholder Report
 6 Months Ended
Jun. 30, 2026
USD ($)
Holding
Shareholder Report [Line Items]  
Document Type N-CSRS
Amendment Flag false
Registrant Name Master Investment Portfolio II
Entity Central Index Key 0001738077
Entity Investment Company Type N-1A
Document Period End Date Jun. 30, 2026
Advantage CoreAlpha Bond Master Portfolio  
Shareholder Report [Line Items]  
Fund Name Advantage CoreAlpha Bond Master Portfolio
Class Name Advantage CoreAlpha Bond Master Portfolio
No Trading Symbol Flag true
Annual or Semi-Annual Statement [Text Block] This semi-annual shareholder report contains important information about Advantage CoreAlpha Bond Master Portfolio (the “Master Portfolio”) for the period of January 1, 2026 to June 30, 2026.
Shareholder Report Annual or Semi-Annual semi-annual shareholder report
Additional Information [Text Block] You can find additional information about the Master Portfolio, which is included within the BlackRock Advantage CoreAlpha Bond Fund’s additional information atblackrock.com/fundreports. You can also request this information by contacting us at (800) 441-7762.
Additional Information Phone Number (800) 441-7762
Additional Information Website blackrock.com/fundreports
Expenses [Text Block]
What were the
Master Portfolio
costs for the
last six months
?
(based on a hypothetical $10,000 investment)
Master Portfolio name
Costs of a $10,000
investment
Costs paid as a percentage of a
$10,000 investment
Advantage CoreAlpha Bond Master Portfolio
$
12		 0.24
%
(a)
(a)
Annualized.
Expenses Paid, Amount $ 12
Expense Ratio, Percent 0.24% [1]
Net Assets $ 634,781,223
Holdings Count | Holding 2,020
Investment Company, Portfolio Turnover 71.00%
Additional Fund Statistics [Text Block]
Key Master Portfolio statistics
Net Assets
$
634,781,223
Number of Portfolio Holdings 2,020
Portfolio Turnover Rate 71
%
Holdings [Text Block]
What did the Master Portfolio invest in?
(as of June 30, 2026)
Portfolio composition
Investment Type
Percent of Total
Investments
(a)
Corporate Bonds 37.3
%
U.S. Government Sponsored Agency Securities 28.6
%
Non-Agency Mortgage-Backed Securities 16.0
%
U.S. Treasury Obligations 11.7
%
Asset-Backed Securities 4.9
%
Foreign Agency Obligations 0.7
%
Municipal Bonds 0.5
%
Capital Trusts 0.3
%
Common Stocks —
%
(b)
Credit quality allocation
Credit Rating
(c)
Percent of Total
Investments
(a)
AAA/Aaa
(d)
 22.9
%
AA/Aa 22.9
%
A 15.0
%
BBB/Baa 25.1
%
BB/Ba 5.7
%
B 2.1
%
CCC/Caa 0.3
%
N/R 6.0
%
(a)
Excludes short-term securities, short investments and options, if any.
(b)
Rounds to less than 0.1%.
(c)
For purposes of this report, credit quality ratings shown above reflect the highest rating assigned by either S&P Global Ratings or Moody’s Investors Service, Inc. if ratings differ. These rating agencies are independent, nationally recognized statistical rating organizations and are widely used. Investment grade ratings are credit ratings of BBB/Baa or higher. Below investment grade ratings are credit ratings of BB/Ba or lower. Investments designated N/R are not rated by either rating agency. Unrated investments do not necessarily indicate low credit quality. Credit quality ratings are subject to change.
(d)
The investment adviser evaluates the credit quality of unrated investments based upon certain factors including, but not limited to, credit ratings for similar investments and financial analysis of sectors, individual investments and/or issuers. Using this approach, the investment adviser has deemed unrated U.S. Government Sponsored Agency Securities and/or U.S. Treasury Obligations to be of similar credit quality as investments rated AAA/Aaa.
Credit Quality Explanation [Text Block] The investment adviser evaluates the credit quality of unrated investments based upon certain factors including, but not limited to, credit ratings for similar investments and financial analysis of sectors, individual investments and/or issuers. Using this approach, the investment adviser has deemed unrated U.S. Government Sponsored Agency Securities and/or U.S. Treasury Obligations to be of similar credit quality as investments rated AAA/Aaa.
Credit Ratings Selection [Text Block] For purposes of this report, credit quality ratings shown above reflect the highest rating assigned by either S&P Global Ratings or Moody’s Investors Service, Inc. if ratings differ. These rating agencies are independent, nationally recognized statistical rating organizations and are widely used. Investment grade ratings are credit ratings of BBB/Baa or higher. Below investment grade ratings are credit ratings of BB/Ba or lower. Investments designated N/R are not rated by either rating agency. Unrated investments do not necessarily indicate low credit quality. Credit quality ratings are subject to change.
[1] Annualized.