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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 surrendered in period.

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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 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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Shares committed to fund long term incentive plans.

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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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Estimated period over which an employee is required to provide service in exchange for the equity-based payment award, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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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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Date the equity-based award expires, in CCYY-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, 2019 shares	Jan. 31, 2020 shares	Jan. 31, 2019 shares	Mar. 31, 2019 shares	Mar. 31, 2018 shares	Mar. 31, 2017 shares	Dec. 31, 2019 USD ($) installment $ / shares shares	Dec. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) shares
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							7,197,212
Fair value of RSUs/restricted stock granted to employees \| $							$ 508	$ 492	$ 421
Fair market value of RSUs/restricted stock converted to common stock \| $							$ 398	$ 443	$ 457
Restricted Stock and RSUs, Granted							1,226,249
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							174,752	155,403	126,906
Intrinsic value of outstanding RSUs \| $							$ 1,100
Stock price \| $ / shares							$ 502.70
Unrecognized stock-based compensation expense \| $							$ 347
Remaining weighted-average period							1 year 1 month 6 days
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							674,206	527,337	699,991
Awards to employees cliff vesting							377,291	209,201	277,313
RSUs to employees that cliff vest, percentage							100.00%	100.00%	100.00%
RSUs to employees that cliff vest, date							Jan. 31, 2022	Jan. 31, 2021	Jan. 31, 2020
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		517,129
Awards to employees cliff vesting		380,335
RSUs to employees that cliff vest, percentage		100.00%
RSUs to employees that cliff vest, date		Jan. 31, 2023
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							283,014
Intrinsic value of outstanding RSUs \| $							$ 373
Stock price \| $ / shares							$ 502.70
Unrecognized stock-based compensation expense \| $							$ 107
Remaining weighted-average period							1 year 1 month 6 days
Awards to employees cliff vesting				283,014	199,068	294,584
RSUs to employees that cliff vest, percentage				100.00%	100.00%	100.00%
RSUs to employees that cliff vest, date				Jan. 31, 2022	Jan. 31, 2021	Jan. 31, 2020
Additional Restricted Stock and RSUs, Granted			2,117				2,117
Fair value of RSUs/restricted stock granted to employees \| $							$ 117	$ 121	$ 111
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		239,415
RSUs to employees that cliff vest, percentage		100.00%
RSUs to employees that cliff vest, date		Jan. 31, 2023
Long-Term Incentive Plans Funded by PNC [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of additional shares surrendered	143,458
Performance-Based Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Remaining weighted-average period							3 years 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
Strike price \| $ / shares							$ 513.50	$ 513.50
Grant-date fair value of awards issued \| $									$ 208
Unrecognized stock-based compensation expense \| $							$ 108
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							5 years
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							6 years
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							7 years
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] \| Long-Term Incentive Plans Funded by PNC [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares committed to fund long-term incentive plans							4,000,000
Maximum [Member] \| Performance-Based Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period, years							9 years