Stock Compensation Plans - Narrative (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Options granted (shares)	4.2
Stpcl option granted, weighted average exercise price per share	$ 10.12
Stock option granted, weighted average fair value per share	$ 1.97
Stock-based compensation expense	$ 6	$ 3
Unearned compensation cost related to the unvested portion of all stock-based awards	$ 39
Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Equity instruments granted (shares)	0.3
Weighted average fair value per share granted (dollars per share)	$ 10.12
Performance Share Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Equity instruments granted (shares)	0.2
Weighted average fair value per share granted (dollars per share)	$ 7.80

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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

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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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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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Gross number of share options (or share units) granted during the period.

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The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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