Stock Based Incentive Compensation Plans (Summary of activity for stock options with service conditions) (Details) - Stock options with service conditions [Member] - USD ($) $ / shares in Units, $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Summary of activity for stock options [Roll Forward]
Outstanding as of beginning of year (in shares)		2,713,058
Granted - original (in shares)		407,637	776,895	502,664
Exercised (includes shares tendered) (in shares)		(840,733)
Forfeited or expired (in shares)		(87,823)
Outstanding as of end of year (in shares)		2,192,139	2,713,058
Vested or expected to vest as of end of year (in shares)	[1]	1,965,675
Exercisable as of end of year (in shares)		1,214,214
Summary of activity for stock options, additional disclosures [Abstract]
Weighted average exercise price as of beginning of year (in dollars per share)		$ 41.97
Weighted average exercise price granted - original (in dollars per share)		71.47
Weighted average exercise price exercised (includes shares tendered) (in dollars per share)		44.64
Weighted average exercise price forfeited or expired (in dollars per share)		52.09
Weighted average exercise price outstanding as of end of year (in dollars per share)		46.02	$ 41.97
Weighted average exercise price vested or expected to vest as of end of year (in dollars per share)	[1]	45.20
Weighted average exercise price exercisable as of end of year (in dollars per share)		$ 40.22
Weighted average remaining contractual term outstanding as of end of year (in years)		7 years 26 days
Weighted average remaining contractual term vested or expected to vest as of end of year (in years)	[1]	6 years 11 months 5 days
Weighted average remaining contractual term exercisable as of end of year (in years)		5 years 11 months 19 days
Aggregate intrinsic value outstanding as of end of year		$ 68
Aggregate intrinsic value vested or expected to vest as of end of year	[1]	62
Aggregate intrinsic value exercisable as of end of year		$ 45

[1] Includes estimated forfeitures.