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Stock-Based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions		1 Months Ended			3 Months Ended			12 Months Ended
	May 30, 2023	Jan. 31, 2024	Jan. 31, 2023	Jan. 31, 2022	Mar. 31, 2023	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock shares authorized for issuance under Award Plan								41,500,000
Number of shares remaining for future awards								2,248,287
Fair value of RSUs granted to employees								$ 565	$ 662	$ 664
Fair market value of RSUs converted to common stock								$ 592	$ 461	$ 391
RSUs, Granted								771,935
Employee stock purchase plan, purchase price percentage								95.00%
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period, years								3 years	3 years	3 years
RSUs, Granted								342,706	498,633	470,253
Intrinsic value of outstanding RSUs								$ 1,400
Stock price								$ 811.8
Unrecognized stock-based compensation expense								$ 421
Remaining weighted-average period								1 year 1 month 6 days
RSUs to employees that cliff vest, percentage								100.00%	100.00%	100.00%
RSUs to employees that cliff vest, date								Jan. 31, 2026	Jan. 31, 2025	Jan. 31, 2024
RSUs, Granted with various vesting schedules								169,764	117,169	168,504
Restricted Stock Units (RSUs) [Member] \| Share-based Payment Arrangement, Tranche One [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards to employees cliff vesting								0	0	247,621
Restricted Stock Units (RSUs) [Member] \| Share-based Payment Arrangement, Tranche Two [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards to employees cliff vesting								0	197,817	0
Restricted Stock Units (RSUs) [Member] \| Share-based Payment Arrangement, Tranche Three [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards to employees cliff vesting								259,465	0	0
RSUs/Restricted Stock [Member] \| Subsequent Event [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period, years		3 years
RSUs, Granted		347,000
Awards to employees cliff vesting		344,000
RSUs to employees that cliff vest, percentage		100.00%
RSUs to employees that cliff vest, date		Jan. 31, 2027
RSUs, Granted with various vesting schedules		6,000
Performance-Based RSUs [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period, years					3 years	3 years	3 years
RSUs, Granted								169,938
Intrinsic value of outstanding RSUs								$ 370
Stock price								$ 811.8
Unrecognized stock-based compensation expense								$ 82
Remaining weighted-average period								1 year 1 month 6 days
Awards to employees cliff vesting					169,938	143,846	162,029
RSUs to employees that cliff vest, percentage					100.00%	100.00%	100.00%
Share based compensation vesting option exercised period	up to nine years							up to nine years
RSUs to employees that cliff vest, date				Jan. 31, 2024	Jan. 31, 2026		Jan. 31, 2023
Additional Restricted Stock and RSUs, Granted			29,194					29,194
Fair value of RSUs/restricted stock granted to employees								$ 142	$ 164	$ 122
Performance-Based RSUs [Member] \| Share-based Payment Arrangement, Tranche One [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
RSUs to employees that cliff vest, percentage	25.00%
RSUs to employees that cliff vest, vesting date	May 30, 2027
Performance-Based RSUs [Member] \| Share-based Payment Arrangement, Tranche Two [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
RSUs to employees that cliff vest, percentage	25.00%
RSUs to employees that cliff vest, vesting date	May 30, 2028
Performance-Based RSUs [Member] \| Share-based Payment Arrangement, Tranche Three [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
RSUs to employees that cliff vest, percentage	50.00%
RSUs to employees that cliff vest, vesting date	May 30, 2029
Performance-Based RSUs [Member] \| Subsequent Event [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period, years		3 years
Awards to employees cliff vesting		166,000
RSUs to employees that cliff vest, percentage		100.00%
RSUs to employees that cliff vest, date		Jan. 31, 2027
Performance-Based Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Remaining weighted-average period								3 years 4 months 24 days
Award vesting percentage of BlackRock's grant-date stock price	130.00%							125.00%
Award vesting period of BlackRock's performance period	3 years
Award vesting period of BlackRock's grant-date stock price	4 years							5 years
Award performance measurement period								4 years
Strike price								$ 513.5
Grant-date fair value of awards issued								$ 120			$ 208
Number of shares awarded to purchase	814,482
Unrecognized stock-based compensation expense								160
Fair value of options vested								56
Aggregate intrinsic value of options exercised								$ 44
Performance-Based Stock Options [Member] \| Share-based Payment Arrangement, Tranche One [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Service period of awards								2022
Performance-Based Stock Options [Member] \| Share-based Payment Arrangement, Tranche Two [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Service period of awards								2023
Performance-Based Stock Options [Member] \| Share-based Payment Arrangement, Tranche Three [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Service period of awards								2024
Two Thousand Twenty Three Performance Based Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Strike price								$ 673.58	$ 0
Time Based Stock Options Member
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation vesting option exercised period	up to nine years
Strike price								$ 673.58
Grant-date fair value of awards issued								$ 55
Number of shares awarded to purchase	326,391
Time Based Stock Options Member \| Share-based Payment Arrangement, Tranche One [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
RSUs to employees that cliff vest, percentage	25.00%
RSUs to employees that cliff vest, vesting date	May 30, 2027
Time Based Stock Options Member \| Share-based Payment Arrangement, Tranche Two [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
RSUs to employees that cliff vest, percentage	25.00%
RSUs to employees that cliff vest, vesting date	May 30, 2028
Time Based Stock Options Member \| Share-based Payment Arrangement, Tranche Three [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
RSUs to employees that cliff vest, percentage	50.00%
RSUs to employees that cliff vest, vesting date	May 30, 2029
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period, years								1 year
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period, years								3 years