Stock-Based Compensation - Stock Option Exercises and Restricted Stock Vesting (Detail) - USD ($) shares in Millions, $ in Millions	9 Months Ended
Sep. 30, 2021	Sep. 30, 2020
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Proceeds from stock option exercises	$ 20	$ 32
Aggregate intrinsic value	44	102
Tax benefit realized upon exercise	$ 11	$ 24
Number of shares exercised (shares)	0.2	0.5
Restricted Stock
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Fair value of shares vested	$ 193	$ 195
Tax benefit realized upon vesting	$ 45	$ 45
Number of shares vested (shares)	0.7	0.8
Performance Based Restricted Stock
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Fair value of shares vested	$ 28	$ 70
Tax benefit realized upon vesting	$ 7	$ 17
Number of shares vested (shares)	0.1	0.3

Amount of tax benefit from vesting of other than stock options granted under share-based compensation arrangement.

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Amount of tax benefit from exercise of option under share-based payment arrangement.

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Amount of cash inflow from exercise of option under share-based payment arrangement.

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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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Number of share options (or share units) exercised during the current period.

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