Share-based Compensation (Equity-Based Compensation Expense) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based compensation expense	$ 32	$ 13	$ 62	$ 82
Tax benefit recognized	5	2	12	10
PRSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based compensation expense	4	2	(8)	25
RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based compensation expense	21	12	58	28
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based compensation expense	8	8	24	25
SARs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total share-based compensation expense	$ (1)	$ (9)	$ (12)	$ 4