Investment Securities - Gains and Losses Related to Investment Securities (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Investments, Debt and Equity Securities [Abstract]
Gross realized gains from sales of available-for-sale securities	$ 15	$ 48	$ 57	$ 64
Gross realized losses from sales of available-for-sale securities	(17)	(48)	(62)	(49)
Gross losses from other-than-temporary impairment	0	0	(1)	(1)
Losses reclassified (from) to other comprehensive income	0	0	0	(10)
Gains (losses) related to investment securities, net	(2)	0	(6)	4
Impairment associated with expected credit losses	0	0	0	(10)
Impairment associated with adverse changes in timing of expected future cash flows	0	0	(1)	(1)
Net impairment losses	$ 0	$ 0	$ (1)	$ (11)