Stock Compensation Plans - Stock-based Compensation Expense (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units	$ 36	$ 19
Stock options	6	4
Employee stock purchase plan	2	2
Stock-based compensation expense	44	25
Tax Benefit	(5)	(3)
Stock-based compensation expense (net of tax)	$ 39	$ 22

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

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Amount, after tax, of expense for award under share-based payment arrangement.

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Amount of tax benefit for recognition of expense of award under share-based payment arrangement.

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The amount of plan compensation cost recognized during the period.

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Amount of noncash expense for award of restricted stock or unit under share-based payment arrangement.

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Amount of noncash expense for option under share-based payment arrangement.

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