Stock-Based Compensation Plans - Summary of Stock Option Activity (Details) - Employee Stock Option [Member] - USD ($) $ / shares in Units, $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
December 31, 2014		18,830,967
Options exercised		(7,133)
Options forfeited		(5,250)
Options expired		(3,245,827)
December 31, 2015		15,572,757
Weighted Average Exercise Price (in usd per share)		$ 46.68	$ 46.85
Options Reinstated, Weighted Average Exercise Price (in usd per share)		21.25
Options Forfeited, Weighted Average Exercise Price (in usd per share)		39.81
Options Expired, Weighted Average Exercise Price (in usd per share)		$ 47.75
Shares Outstanding, Weighted Average Remaining Contractual Life		3 years 10 months 6 days
Shares Outstanding, Aggregate Intrinsic Value		$ 9
Exercisable at December 31, 2014	[1]	15,490,507
Shares Exercisable, Weighted Average Exercise Price (in usd per share)	[1]	$ 46.72
Shares Exercisable, Weighted Average Remaining Contractual Life	[1]	3 years 10 months 2 days
Shares Exercisable, Aggregate Intrinsic Value	[1]	$ 9

[1] Includes stock options issued to retirement eligible employees.