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Fair value of restricted stock units and restricted stock that vested and converted to common stock.

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Share based compensation arrangement by share based payment award performance measurement period.

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Share based compensation arrangement by share based payment award award vesting rights of grant period.

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Share-based compensation arrangement by share-based payment award vesting rights percentage of grant date stock price.

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The number of additional grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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Share based compensation arrangement by share based payment award equity instruments other than options granted in period fair value.

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Share based compensation arrangement by share based payment award equity instruments other than options grants in period with various vesting schedules.

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Share based compensation arrangement by share based payment award equity instruments other than options that cliff vest.

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Share-based compensation arrangement by share based payment award, number of shares remaining

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Share-based compensation arrangement by share-based payment award options grant date fair value.

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Share based compensation arrangement by share based payment award requisite service year.

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Share-based compensation arrangement by share-based payment award vesting number of installments.

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Share-based compensation, employee stock purchase plan, purchase price percentage of fair market value for eligible employees

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Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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Amount of cost to be recognized for nonvested award under share-based payment arrangement. Excludes share and unit options.

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Amount of cost to be recognized for option under share-based payment arrangement.

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Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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Weighted average remaining contractual term for equity-based awards excluding options, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Date the equity-based award expires, in YYYY-MM-DD format.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Number of shares authorized for issuance under share-based payment arrangement.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Price of a single share of a number of saleable stocks of a company.

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Percentage of vesting of award under share-based payment arrangement.

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Intrinsic value of outstanding award under share-based payment arrangement. Excludes share and unit options.

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Stock-Based Compensation - Additional Information (Detail) $ / shares in Units, $ in Millions	1 Months Ended		3 Months Ended			12 Months Ended
	Jan. 31, 2022 shares	Jan. 31, 2021 shares	Mar. 31, 2021 shares	Mar. 31, 2020 shares	Mar. 31, 2019 shares	Dec. 31, 2021 USD ($) installment $ / shares shares	Dec. 31, 2020 USD ($) $ / shares shares	Dec. 31, 2019 USD ($) shares	Dec. 31, 2017 USD ($)
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						5,190,152
Fair value of RSUs/restricted stock granted to employees \| $						$ 664	$ 517	$ 508
Fair market value of RSUs/restricted stock converted to common stock \| $						$ 391	$ 421	$ 398
Restricted Stock and RSUs, Granted						886,378
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]
Restricted Stock and RSUs, Granted						168,504	71,531	174,752
Intrinsic value of outstanding RSUs \| $						$ 2,000
Stock price \| $ / shares						$ 915.56
Unrecognized stock-based compensation expense \| $						$ 472
Remaining weighted-average period						1 year
RSUs/Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period, years						3 years	3 years	3 years
Restricted Stock and RSUs, Granted						470,253	504,403	674,206
Awards to employees cliff vesting						247,621	393,161	377,291
RSUs to employees that cliff vest, percentage						100.00%	100.00%	100.00%
RSUs to employees that cliff vest, date						Jan. 31, 2024	Jan. 31, 2023	Jan. 31, 2022
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 and RSUs, Granted	498,633
Awards to employees cliff vesting	197,817
RSUs to employees that cliff vest, percentage	100.00%
RSUs to employees that cliff vest, date	Jan. 31, 2025
Restricted Stock and RSUs, Granted with various vesting schedules	8,612
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
Restricted Stock and RSUs, Granted						162,029
Intrinsic value of outstanding RSUs \| $						$ 612
Stock price \| $ / shares						$ 915.56
Unrecognized stock-based compensation expense \| $						$ 169
Remaining weighted-average period						1 year
Awards to employees cliff vesting			162,029	238,478	283,014
RSUs to employees that cliff vest, percentage			100.00%	100.00%	100.00%
RSUs to employees that cliff vest, date			Jan. 31, 2024	Jan. 31, 2023	Jan. 31, 2022
Additional Restricted Stock and RSUs, Granted		4,545				4,545
Fair value of RSUs/restricted stock granted to employees \| $						$ 122	$ 139	$ 117
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	143,846
RSUs to employees that cliff vest, percentage	100.00%
RSUs to employees that cliff vest, date	Jan. 31, 2025
Performance-Based Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Remaining weighted-average period						1 year 10 months 24 days
Award vesting percentage of BlackRock's grant-date stock price						125.00%
Award vesting period of BlackRock's grant-date stock price						5 years
Award performance measurement period						4 years
Award vesting, number of equal installments \| installment						3
Weighted average remaining life of awards						4 years 10 months 24 days
Strike price \| $ / shares						$ 513.50	$ 513.50
Grant-date fair value of awards issued \| $									$ 208
Unrecognized stock-based compensation expense \| $						$ 49
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
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
Maximum [Member] \| Performance-Based Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period, years						9 years