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Leases - Schedule of Supplemental Information Related to Operating Leases (Parenthetical) (Detail) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Operating Leased Assets [Line Items]
Operating lease ROU assets	$ 1,874	$ 1,519
Global Infrastructure Management, LLC [Member]
Operating Leased Assets [Line Items]
Operating lease ROU assets	$ 178	$ 75

X

- Definition

Amount of lessee's right to use underlying asset under operating lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 842
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479041/842-20-45-1

+ Details

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

X

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_OperatingLeasedAssetsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Details

Name:	us-gaap_BusinessAcquisitionAxis=blk_GlobalInfrastructureManagementLLCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: