Share-based Incentive Compensation Plans - Compensation Cost (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]
Compensation cost	$ 17	$ 20	$ 55	$ 56
Income tax benefit	4	19	23	20
After-tax share-based compensation expense	13	1	32	36
Restricted Stock Unit (RSU) awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost	9	10	27	27
Performance Stock Unit (PSU) awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost	7	8	25	25
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost	$ 1	$ 2	$ 3	$ 4

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

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