Stock Compensation Plans - Narrative (Details) - USD ($) $ / shares in Thousands, shares in Millions, $ in Millions	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock-based compensation expense	$ 4	$ 6
Unearned compensation cost related to the unvested portion of all stock-based awards	$ 29
Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Equity instruments granted (shares)	0.5
Weighted average fair value per share granted (dollars per share)	$ 16,300
Performance Share Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Equity instruments granted (shares)	0.1
Weighted average fair value per share granted (dollars per share)	$ 19,210

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

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-Name Accounting Standards Codification
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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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