Earnings Per Common Share - Computation of Basic and Diluted Earnings Per Share (Details) (USD $) In Millions, except Share data in Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Earnings Per Share [Abstract]
Net income	$ 409	$ 363
Preferred stock dividends	(31)	(6)
Dividends and undistributed earnings allocated to participating securities(1)	(1)	(1)
Net income available to common shareholders	$ 377	$ 356
Basic (in shares)	412,225	430,621
Effect of dilutive securities: common stock options and common stock awards	6,525	8,194
Diluted average common shares	418,750	438,815
Anti-dilutive securities (in shares)	791	1,504
Earnings per Common Share:
Basic (in dollars per share)	$ 0.91	$ 0.83
Diluted (in dollars per share)	$ 0.90	$ 0.81