Stock Plans and Share-Based Compensation - Share-Based Compensation and Related Income Tax Benefit (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Share-based Compensation Expense	$ 29	$ 74	$ 51
Income Tax Benefit	19	43	26
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Share-based Compensation Expense	19	18	13
Restricted Stock Units and Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Share-based Compensation Expense	6	8	6
Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Share-based Compensation Expense	5	4	2
Stock Awards for Directors
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Share-based Compensation Expense	2	2	2
Performance Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Share-based Compensation Expense	$ (3)	$ 42	$ 28