Stock-based Compensation Plans (Schedule of Stock-based Compensation) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 171	$ 166	$ 160
Stock-based tax benefit recognized	35	29	30
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	99	98	94
Stock-based tax benefit recognized	30	39	63
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	35	32	28
Long-Term Performance Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	37	36	38
Stock-based tax benefit recognized	$ 10	$ 24	$ 15