Earnings Per Common Share - Computation of Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Earnings Per Share [Abstract]
Net income	$ 422	$ 622	$ 831	$ 985
Preferred stock dividends	(29)	(19)	(60)	(25)
Dividends and undistributed earnings allocated to participating securities(1)	0	(1)	(1)	(2)
Net income available to common shareholders	$ 393	$ 602	$ 770	$ 958
Basic (in shares)	410,674	427,824	411,445	429,215
Effect of dilutive securities: common stock options and common stock awards	6,038	7,496	6,198	7,743
Diluted average common shares	416,712	435,320	417,643	436,958
Anti-dilutive securities (in shares)	619	1,508	704	1,506
Earnings per Common Share:
Basic (in dollars per share)	$ 0.96	$ 1.41	$ 1.87	$ 2.23
Diluted (in dollars per share)	$ 0.94	$ 1.38	$ 1.84	$ 2.19