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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
		Jul. 01, 2025	May 30, 2023	Jan. 31, 2026	Jul. 31, 2025	Oct. 31, 2024	Mar. 31, 2025	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock shares authorized for issuance under Award Plan										48,500,000
Number of shares remaining for future awards										6,154,871
Weighted-Average Grant Date Fair Value, Granted										$ 991.2
Fair value of RSUs granted to employees										$ 1,700.0	$ 1,100.0	$ 565.0
Fair market value of RSUs converted to common stock										$ 517.0	$ 592.0	$ 592.0
Restricted Stock Units, Granted										168,731
Awards vesting										54,212
Reduction of shares due to performance measures										(71,866)
Employee stock purchase plan, purchase price percentage										95.00%
HPS Transaction [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted Stock Units, Granted					680,000
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										5 years
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
Restricted Stock Units, Granted										369,169	346,831	342,706
Intrinsic value of outstanding RSUs										$ 3,500.0
Stock price										$ 1,070
Unrecognized stock-based compensation expense										$ 1.4
Remaining weighted-average period										2 years
RSUs to employees that cliff vest, percentage										100.00%	100.00%	100.00%
RSUs, Granted with various vesting schedules										173,599	204,622	169,764
Restricted Stock Units (RSUs) [Member] | HPS Transaction [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-Average Grant Date Fair Value, Granted					$ 991.52
Award vesting period					5 years
Restricted Stock Units, Granted										394,000,000
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	[1]									269,930	0	0
RSUs to employees that cliff vest, date													Dec. 31, 2025
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	0	259,465
RSUs to employees that cliff vest, date												Jan. 31, 2026
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										0	343,418	0
RSUs to employees that cliff vest, date											Jan. 31, 2027
Restricted Stock Units (RSUs) [Member] | GIP Transaction [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted Stock Units, Granted										142,000,000	71,000,000
RSUs/Restricted Stock [Member] | Subsequent Event [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period, years				3 years
Restricted Stock Units, Granted				342,000
Awards to employees cliff vesting				320,000
RSUs to employees that cliff vest, percentage				100.00%
RSUs to employees that cliff vest, date				Jan. 31, 2029
RSUs, Granted with various vesting schedules				36,000
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
Weighted-Average Grant Date Fair Value, Granted										$ 991.38
Restricted Stock Units, Granted										167,962
Intrinsic value of outstanding RSUs										$ 726.0
Awards vesting										54,212
Stock price										$ 1,070
Unrecognized stock-based compensation expense										$ 290.0
Remaining weighted-average period										1 year 10 months 24 days
Awards to employees cliff vesting							136,000	166,000	170,000
RSUs to employees that cliff vest, percentage							100.00%	100.00%	100.00%
Share based compensation vesting option exercised period										up to nine years
RSUs to employees that cliff vest, date							Jan. 31, 2028	Jan. 31, 2027	Jan. 31, 2026
Reduction of shares due to performance measures										(71,866)
Fair value of RSUs/restricted stock granted to employees										$ 107.0	$ 279.0	$ 142.0
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				137,000
RSUs to employees that cliff vest, percentage				100.00%
RSUs to employees that cliff vest, date				Jan. 31, 2029
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] | GIP Transaction [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-Average Grant Date Fair Value, Granted										$ 952.02
Restricted Stock Units, Granted										769
Awards vesting						210,000				0
Reduction of shares due to performance measures										0
Performance-Based Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Remaining weighted-average period										2 years 8 months 12 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												$ 120.0		$ 208.0
Number of shares awarded to purchase			814,482
Unrecognized stock-based compensation expense										$ 72.0
Aggregate intrinsic value of options exercised										$ 171.0
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
2023 Performance-based Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Strike price										$ 673.58	$ 673.58
Time Based Stock Options Member
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Remaining weighted-average period										2 years 8 months 12 days
Share based compensation vesting option exercised period			up to nine years
Strike price										$ 673.58
Grant-date fair value of awards issued										$ 55.0
Number of shares awarded to purchase			326,391
Unrecognized stock-based compensation expense										$ 72.0
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
Cliff vesting RSU [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
RSUs to employees that cliff vest, percentage		100.00%
Cliff vesting RSU [Member] | HPS Transaction [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted Stock Units, Granted					270,000
RSUs to employees that cliff vest, percentage										100.00%
Weighted-Average Grant Date Fair Value, Granted					$ 957.42
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