Share-Based Compensation Plans - Summary of Information Relative to Stock Option Plan Activity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Number of Options, Outstanding, January 1 (in shares)	76,135
Number of Options, Granted (in shares)	5,565
Number of Options, Exercised (in shares)	(13,779)
Number of Options, Forfeited (in shares)	(3,253)
Number of Options, Outstanding, December 31 (in shares)	64,668	76,135
Number of Options, Exercisable (in shares)	54,990
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Weighted Average Exercise Price, Options Outstanding, January 1 (in dollars per share)	$ 39.05
Weighted Average Exercise Price, Granted (in dollars per share)	59.73	$ 58.14	$ 45.01
Weighted Average Exercise Price, Exercised (in dollars per share)	35.23
Weighted Average Exercise Price, Forfeited (in dollars per share)	39.10
Weighted Average Exercise Price, Options Outstanding, December 31 (in dollars per share)	41.64	$ 39.05
Weighted Average Exercise Price, Exercisable (in dollars per share)	$ 39.12
Weighted Average Remaining Contractual Term, Outstanding	3 years 8 months 15 days
Weighted Average Remaining Contractual Term, Exercisable	2 years 10 months 15 days
Aggregate Intrinsic Value, Outstanding	$ 785
Aggregate Intrinsic Value, Exercisable	$ 765