Shareholder Report

6 Months Ended

Jun. 30, 2026

USD ($)

Holding

Shareholder Report [Line Items]

N-CSRS

false

Registrant Name

BlackRock Series Fund, Inc.

Entity Central Index Key

0000319108

Entity Investment Company Type

N-1A

Document Period End Date

Jun. 30, 2026

Shareholder Report [Line Items]

BlackRock Advantage Large Cap Core Portfolio

LGCCS

Annual or Semi-Annual Statement [Text Block]

This semi-annual shareholder report contains important information about BlackRock Advantage Large Cap Core Portfolio (the “Fund”) 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 Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 537-4942.

Additional Information Website

blackrock.com/fundreports

Expenses [Text Block]

What were the Fund costs for the last six months?

(based on a hypothetical $10,000 investment)

Table Summary
Fund name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
BlackRock Advantage Large Cap Core Portfolio	$25	0.48%^{Footnote Reference(a)}

Footnote	Description
Footnote^(a)	Annualized.

Expenses Paid, Amount

$ 25

Expense Ratio, Percent

0.48%

^[1]

$ 234,943,175

Holdings Count | Holding

291

InvestmentCompanyPortfolioTurnover

55.00%

Holdings [Text Block]

Sector allocation

Table Summary
Sector^{Footnote Reference(a)}	Percent of Net Assets
Information Technology........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	36.4%
Industrials........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	11.6
Financials........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	11.4
Consumer Discretionary........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	9.9
Communication Services........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	9.7
Health Care........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	9.3
Energy........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	3.3
Consumer Staples........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	3.2
Materials........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	1.8
Utilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	1.4
Real Estate........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	1.0
Short-Term Securities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	2.4
Liabilities in Excess of Other Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	(1.4)

Footnote	Description
Footnote^(a)	For purposes of this report, sector sub-classifications may differ from those utilized by the Fund for compliance purposes.

Shareholder Report [Line Items]

BlackRock Balanced Portfolio

BLCPS

Annual or Semi-Annual Statement [Text Block]

This semi-annual shareholder report contains important information about BlackRock Balanced Portfolio (the “Fund”) 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 Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 537-4942.

Additional Information Website

blackrock.com/fundreports

Expenses [Text Block]

What were the Fund costs for the last six months?

(based on a hypothetical $10,000 investment)

Table Summary
Fund name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
BlackRock Balanced Portfolio	$25	0.48%^{Footnote Reference(a)}

Footnote	Description
Footnote^(a)	Annualized.

Expenses Paid, Amount

$ 25

Expense Ratio, Percent

0.48%

^[2]

$ 489,871,071

Holdings Count | Holding

2,121

InvestmentCompanyPortfolioTurnover

74.00%

Holdings [Text Block]

Portfolio composition

Table Summary
Investment Type	Percent of Total Investments^{Footnote Reference(a)}
Common Stocks........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	55.3%
Corporate Bonds........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	19.2
U.S. Government Sponsored Agency Securities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	13.2
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	10.2
Non-Agency Mortgage-Backed Securities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	1.2
Asset-Backed Securities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	0.4
Foreign Government Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	0.3
Preferred Securities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	0.2
Rights........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	0.0^{Footnote Reference(b)}
Other Interests........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	-

Footnote	Description
Footnote^(a)	Excludes short-term securities, short investments and options, if any.
Footnote^(b)	Rounds to less than 0.1%.

Shareholder Report [Line Items]

BlackRock Capital Appreciation Portfolio

FDGRS

Annual or Semi-Annual Statement [Text Block]

This semi-annual shareholder report contains important information about BlackRock Capital Appreciation Portfolio (the “Fund”) 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 Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 537-4942.

Additional Information Website

blackrock.com/fundreports

Expenses [Text Block]

What were the Fund costs for the last six months?

(based on a hypothetical $10,000 investment)

Table Summary
Fund name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
BlackRock Capital Appreciation Portfolio	$25	0.47%^{Footnote Reference(a)}

Footnote	Description
Footnote^(a)	Annualized.

Expenses Paid, Amount

$ 25

Expense Ratio, Percent

0.47%

^[3]

$ 278,341,588

Holdings Count | Holding

34

InvestmentCompanyPortfolioTurnover

50.00%

Holdings [Text Block]

Sector allocation

Table Summary
Sector^{Footnote Reference(a)}	Percent of Net Assets
Information Technology........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	52.3%
Industrials........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	15.0
Communication Services........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	11.6
Consumer Discretionary........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	8.3
Real Estate........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	4.1
Health Care........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	3.2
Energy........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	2.5
Materials........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	1.8
Consumer Staples........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	0.9
Short-Term Securities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	0.1
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	0.2

Footnote	Description
Footnote^(a)	For purposes of this report, sector sub-classifications may differ from those utilized by the Fund for compliance purposes.

Shareholder Report [Line Items]

BlackRock Global Allocation Portfolio

GLALS

Annual or Semi-Annual Statement [Text Block]

This semi-annual shareholder report contains important information about BlackRock Global Allocation Portfolio (the “Fund”) 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 Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 537-4942.

Material Fund Change Notice [Text Block]

Additional Information Website

blackrock.com/fundreports

Expenses [Text Block]

What were the Fund costs for the last six months?

(based on a hypothetical $10,000 investment)

Table Summary
Fund name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
BlackRock Global Allocation Portfolio	$30	0.57%^{Footnote Reference(a)}

Footnote	Description
Footnote^(a)	Annualized.

Expenses Paid, Amount

$ 30

Expense Ratio, Percent

0.57%

^[4]

$ 167,818,438

Holdings Count | Holding

2,035

InvestmentCompanyPortfolioTurnover

80.00%

Additional Fund Statistics [Text Block]

Key Fund statistics

Table Summary
Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	$167,818,438
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	2,035
Portfolio Turnover Rate........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	80%

Holdings [Text Block]

Geographic allocation

Table Summary
Country/Geographic Region	Long	Short	Total
	Percent of Total Investments^{Footnote Reference(a)}
United States........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	67.0%	-%	67.0%
United Kingdom........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	4.5	-	4.5
Germany........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	2.8	-	2.8
Ireland........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	2.6	-	2.6
France........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	2.3	-	2.3
Japan........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	2.3	-	2.3
Taiwan........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	2.2	-	2.2
Netherlands........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	2.0	-	2.0
Italy........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	1.9	-	1.9
Canada........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	1.6	-	1.6
Other^{Footnote Reference(b)}........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	10.8	-	10.8
Total........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	100.0%	-%	100.0%

Footnote	Description
Footnote^(a)	Includes the gross market value of long and short securities and excludes short-term securities and options, if any.
Footnote^(b)	Ten largest countries/geographic regions are presented. Additional countries/geographic regions are found in Other.

Shareholder Report [Line Items]

BlackRock Government Money Market Portfolio

MNRSV

Annual or Semi-Annual Statement [Text Block]

This semi-annual shareholder report contains important information about BlackRock Government Money Market Portfolio (the “Fund”) 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 Fund at blackrock.com/fundreports. You can also request this information by contacting us at (800) 537-4942.

Additional Information Website

blackrock.com/fundreports

Expenses [Text Block]

What were the Fund costs for the last six months?

(based on a hypothetical $10,000 investment)

Table Summary
Fund name	Costs of a $10,000 investment	Costs paid as a percentage of a $10,000 investment
BlackRock Government Money Market Portfolio	$22	0.43%^{Footnote Reference(a)}

Footnote	Description
Footnote^(a)	Annualized.

Expenses Paid, Amount

$ 22

Expense Ratio, Percent

0.43%

^[5]

$ 106,562,261

Holdings Count | Holding

153

Additional Fund Statistics [Text Block]

Key Fund statistics

Table Summary
Net Assets........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	$106,562,261
Number of Portfolio Holdings........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	153
Current seven-day yields as of June 30, 2026 (The 7-Day SEC Yield may differ from the 7-Day Yield shown due to the fact that the 7-Day SEC Yield excludes distributed capital gains.)	0
7-Day SEC Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	3.27%
7-Day Yield........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	3.27%

Holdings [Text Block]

Portfolio composition

Table Summary
Asset Type	Percent of Net Assets
Repurchase Agreements........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	36.4%
U.S. Government Sponsored Agency Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	31.9
U.S. Treasury Obligations........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	31.7
Other Assets Less Liabilities........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................	0.0^{Footnote Reference(a)}

Footnote	Description
Footnote^(a)	Rounds to less than 0.1%.

[1]	Annualized.
[2]	Annualized.
[3]	Annualized.
[4]	Annualized.
[5]	Annualized.