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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
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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 |  |  |  |  |  |  |  |  |
[1] | Includes incentive retention awards granted in connection with the HPS and GIP Transactions.

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