Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2022	Mar. 31, 2021
Income Tax Disclosure [Abstract]
Income tax expense benefit net noncash related to revaluation of deferred tax assets and liabilities	$ 18
Discrete income tax expense (benefit)	$ 133	$ 39

Income tax expense benefit net noncash related to revaluation of deferred tax assets and liabilities.

No definition available.

Name:	blk_IncomeTaxExpenseBenefitNetNoncashRelatedToRevaluationOfDeferredTaxAssetsAndLiabilities
Namespace Prefix:	blk_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration