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Stock-Based Compensation - Supplemental Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Stock-Based Compensation
Minimum tax withholdings	$ 27	$ 36	$ 19
Compensation Expense	27	32	41
Tax detriment recognized	(9)	(12)	(4)
Unrecognized Total Cost	23
RSUs
Stock-Based Compensation
Compensation Expense	9	9	12
Unrecognized Total Cost	$ 7
Weighted Average Recognition Period Remaining (In years)	1 year 1 month 24 days
Award vesting period	3 years
DSUs
Stock-Based Compensation
Compensation Expense	$ 2	2	2
Unrecognized Total Cost	$ 0
Weighted Average Recognition Period Remaining (In years)	0 years
MSUs
Stock-Based Compensation
Compensation Expense	$ 0	0	4
Unrecognized Total Cost	$ 0
Weighted Average Recognition Period Remaining (In years)	3 days
RPSUs
Stock-Based Compensation
Compensation Expense	$ 10	10	7
Unrecognized Total Cost	$ 10
Weighted Average Recognition Period Remaining (In years)	11 months 12 days
Award vesting period	3 years
PRSUs
Stock-Based Compensation
Compensation Expense	$ 6	$ 11	$ 16
Unrecognized Total Cost	$ 6
Weighted Average Recognition Period Remaining (In years)	1 year 2 months 26 days
Award vesting period	3 years

X

- Definition

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

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