Stock-Based Compensation - Annual Activity Of Stock Units and Cash Units Additional Information (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Issued During Period, Value, Restricted Stock Award, Gross	$ 19	$ 18	$ 20
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested in Period, Fair Value		$ 1	$ 8
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount	$ 17
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term	1 year
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period	435
Weighted Average Grant Price - Granted	$ 23.14	$ 34.14	$ 48.41
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term	10 months 24 days
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period	73
Number Of Restricted Stock Units Target Award Vested Range Maximum	20.00%
Weighted Average Grant Price - Granted	$ 21.06	$ 34.56	$ 48.52
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Aggregate Intrinsic Value, Outstanding	$ 37
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term	2 years 6 months

Number Of Restricted Stock Units Target Award Vested Range Maximum

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Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Expected to Vest, Weighted Average Remaining Contractual Term

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- Definition

Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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The weighted average fair value at grant date for nonvested equity-based awards issued 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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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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

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- Definition

Aggregate value of stock related to Restricted Stock Awards issued during the period.

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