Investment Securities - Narrative (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015 USD ($)	Jun. 30, 2014 USD ($)	Jun. 30, 2015 USD ($) security	Jun. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)
Investments, Debt and Equity Securities [Abstract]
Pledged Financial Instruments, Not Separately Reported, Securities	$ 38,120		$ 38,120		$ 44,020
Other-than-temporary impairment recorded	0	$ (2)	(1)	$ (11)
Impairment associated with adverse changes in timing of expected future cash flows	0	(1)	(1)	(1)
Impairment associated with expected credit losses	$ 0	$ (1)	0	$ (10)
Gross pre-tax unrealized losses on securities			$ 600
Number of available for sale and held to maturity securities in gross pre-tax unrealized loss position | security			1,447