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		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Earnings Per Share [Abstract]
Net income	$ 585	$ 560	$ 1,416	$ 1,545
Preferred stock dividends	(42)	(18)	(102)	(43)
Dividends and undistributed earnings allocated to participating securities(1)	0	0	(1)	(2)
Net income available to common shareholders	$ 543	$ 542	$ 1,313	$ 1,500
Basic (in shares)	406,612	421,974	409,816	426,775
Effect of dilutive securities: common stock options and common stock awards	5,555	7,762	5,956	7,735
Diluted average common shares	412,167	429,736	415,772	434,510
Anti-dilutive securities (in shares)	619	876	675	1,502
Earnings per Common Share:
Basic (in dollars per share)	$ 1.34	$ 1.28	$ 3.20	$ 3.52
Diluted (in dollars per share)	$ 1.32	$ 1.26	$ 3.16	$ 3.45