Stock Plans and Share-Based Compensation - Share-Based Compensation (Benefit) Expense and Related Income Tax Benefit (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]
Total Share-Based Compensation (Benefit) Expense	$ (12)	$ 17	$ 12	$ 30
Income Tax Benefit	2	7	11	35
Performance Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Share-Based Compensation (Benefit) Expense	(17)	9	(8)	15
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Share-Based Compensation (Benefit) Expense	3	5	13	7
Restricted Stock Units and Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Share-Based Compensation (Benefit) Expense	1	2	3	4
Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Share-Based Compensation (Benefit) Expense	1	1	2	2
Stock Awards for Directors
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Share-Based Compensation (Benefit) Expense	$ 0	$ 0	$ 2	$ 2