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Reference 6: http://www.xbrl.org/2009/role/commonPracticeRef
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Acquisitions - Additional Information (Detail) $ / shares in Units, $ in Millions, £ in Billions				3 Months Ended		9 Months Ended		12 Months Ended
	Jul. 01, 2025 USD ($) $ / shares shares	Mar. 03, 2025 USD ($)	Mar. 03, 2025 GBP (£)	Sep. 30, 2026 USD ($) $ / shares shares	Sep. 30, 2025 USD ($)	Sep. 30, 2026 USD ($) $ / shares shares	Sep. 30, 2025 USD ($)	Dec. 31, 2025 USD ($) shares	Jul. 01, 2026 USD ($)
Business Acquisition [Line Items]
Issuance of common share in connection with acquisition \| $					$ 5,734		$ 5,734
Contingent consideration liabilities \| $				$ 5,858		$ 5,858		$ 8,429
Common stock, shares issued				156,276,289		156,276,289		156,276,289
Restricted Stock Units (RSUs) [Member]
Business Acquisition [Line Items]
Stock price \| $ / shares				$ 1,058		$ 1,058
Cliff Vesting RSU [Member]
Business Acquisition [Line Items]
RSUs to employees that cliff vest, percentage								100.00%
Subco Units [Member]
Business Acquisition [Line Items]
Number of shares issued	8,500,000
Maximum [Member] \| Subco Units [Member]
Business Acquisition [Line Items]
Contingent payments	4,400,000
Minimum [Member] \| Subco Units [Member]
Business Acquisition [Line Items]
Contingent payments	2,800,000
Hps Investment Partners [Member]
Business Acquisition [Line Items]
Date of acquisition	Jul. 01, 2025
Business acquisition, percentage of equity interest acquired	100.00%
Contingent consideration liabilities \| $	$ 3,400
Restricted Stock Units, Granted	680,000
Hps Investment Partners [Member] \| Restricted Stock Units (RSUs) [Member]
Business Acquisition [Line Items]
Award vesting period	5 years
Granted incentive retention awards \| $	$ 675
Hps Investment Partners [Member] \| Cliff Vesting RSU [Member]
Business Acquisition [Line Items]
Restricted Stock Units, Granted	270,000
Granted incentive retention awards \| $	$ 260
Hps Investment Partners [Member] \| Common Stock [Member]
Business Acquisition [Line Items]
Stock price \| $ / shares	$ 1,049
Hps Investment Partners [Member] \| Subco Units [Member]
Business Acquisition [Line Items]
Number of shares issued	8,500,000
Issuance of common share in connection with acquisition \| $	$ 8,500
Contingent payments				2,800,000
Contingent consideration liability fair value \| $				$ 2,600		$ 2,600			$ 2,600
Hps Investment Partners [Member] \| Maximum [Member]
Business Acquisition [Line Items]
Common stock, shares issued	13,800,000
Hps Investment Partners [Member] \| Maximum [Member] \| Subco Units [Member]
Business Acquisition [Line Items]
Contingent payments	4,400,000					4,400,000
Hps Investment Partners [Member] \| Minimum [Member] \| Subco Units [Member]
Business Acquisition [Line Items]
Contingent payments	2,800,000					2,800,000
Preqin Holding Limited [Member]
Business Acquisition [Line Items]
Cash paid		$ 3,219	£ 2.5
Description of acquisition		On March 3, 2025, BlackRock completed the acquisition of 100% of the shares of Preqin Holding Limited (the "Preqin Transaction" or "Preqin"), a leading provider of private markets data, for £2.5 billion (or approximately $3.2 billion) in cash.	On March 3, 2025, BlackRock completed the acquisition of 100% of the shares of Preqin Holding Limited (the "Preqin Transaction" or "Preqin"), a leading provider of private markets data, for £2.5 billion (or approximately $3.2 billion) in cash.
Business acquisition, percentage of equity interest acquired		100.00%	100.00%