Securities - Realized Gains and Losses (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract]
Net gains on sales of AFS debt securities			$ 436	$ 759
Debt securities
Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract]
Gross gains	$ 170	$ 383	445	761
Gross losses	(2)	(1)	(9)	(2)
Net gains on sales of AFS debt securities	168	382	436	759
Income tax expense attributable to realized net gains on sales of AFS debt securities	$ 64	$ 145	$ 166	$ 288