Stock Compensation Plans - Stock-based Compensation Expense (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units	$ 30	$ 23	$ 96	$ 55
Stock options	6	6	17	16
Employee stock purchase plan	2	2	6	5
Stock-based compensation expense	38	31	119	76
Tax Benefit	(5)	(4)	(14)	(9)
Stock-based compensation expense (net of tax)	$ 33	$ 27	$ 105	$ 67

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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