Share-Based Compensation Plans (Summary of Stock Unit Activity) (Details) - Restricted Stock Units (RSUs) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Stock Units
Outstanding, beginning of period (in shares)	2,259,829
Granted (in shares)	1,001,899
Forfeited (in shares)	(50,192)
Issued (in shares)	(836,952)
Outstanding, end of period (in shares)	2,374,584	2,259,829
Not Vested, end of period (in shares)	1,619,720
Weighted-Average Grant-Date Fair Value
Outstanding, beginning of period (in dollars per share)	$ 84.52
Granted (in dollars per share)	95.16	$ 96.16	$ 78.49
Forfeited (in dollars per share)	95.21
Issued (in dollars per share)	79.73
Outstanding, end of period (in dollars per share)	90.47	$ 84.52
Not Vested, end of period (in dollars per share)	$ 91.04
Total Fair Value, Issued	$ 80	$ 102	$ 85