Stock Compensation Plans - Stock-based Compensation Expense (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units	$ 13	$ 22	$ 32	$ 42
Stock options	6	2	10	4
Employee stock purchase plan	1	1	3	2
Stock-based compensation expense	20	25	45	48
Tax benefit	(2)	(4)	(5)	(7)
Stock-based compensation expense (net of tax)	$ 18	$ 21	$ 40	$ 41

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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