Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024
Significant Accounting Policies [Line Items]
Fair value of loaned securities held	$ 10,100	$ 9,900
Fair value of collateral loan under these securities lending agreements	11,000	10,600
Separate account collateral held under securities lending agreements	5,803	6,059
Fair value of securities received as collateral have been resold or repledged	$ 0	$ 0
Minimum [Member]
Significant Accounting Policies [Line Items]
Collateral cash and securities received in exchange of value of securities lent in order to reduce counterparty risk	102.00%
Maximum [Member]
Significant Accounting Policies [Line Items]
Collateral cash and securities received in exchange of value of securities lent in order to reduce counterparty risk	112.00%

Collateral cash and securities received in exchange of value of securities lent in order to reduce credit risk.

No definition available.

Name:	blk_CollateralCashAndSecuritiesReceivedInExchangeOfValueOfSecuritiesLentInOrderToReduceCreditRisk
Namespace Prefix:	blk_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Separate account collateral held under securities lending agreements.

+ References

No definition available.

+ Details

Name:	blk_SeparateAccountCollateralHeldUnderSecuritiesLendingAgreements
Namespace Prefix:	blk_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair Value of Separate Account Collateral obtained under securities lending agreements.

+ References

No definition available.

+ Details

Name:	blk_SeparateAccountFairValueOfCollateralUnderSecuritiesLendingAgreements
Namespace Prefix:	blk_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Significant accounting policies.

+ References

No definition available.

+ Details

Name:	blk_SignificantAccountingPoliciesLineItems
Namespace Prefix:	blk_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Fair value of the collateral, or portion thereof, that has been re-pledged, delivered, or otherwise used.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 860
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 1A
-Subparagraph (c)(2)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481420/860-30-50-1A

+ Details

Name:	us-gaap_FairValueOfSecuritiesReceivedAsCollateralThatHaveBeenResoldOrRepledged
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value portion of securities that an entity sells and agrees to repurchase at a specified date for a specified price.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2E
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-2E

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-2

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-2

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 825
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 10
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482907/825-10-50-10

+ Details

Name:	us-gaap_SecuritiesLoanedOrSoldUnderAgreementsToRepurchaseFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: