Investment Securities - Narrative (Details) (USD $)	3 Months Ended
	Mar. 31, 2015 security	Mar. 31, 2014	Dec. 31, 2014
Investments, Debt and Equity Securities [Abstract]
Pledged Financial Instruments, Not Separately Reported, Securities	$ 43,000,000,000		$ 44,020,000,000
Other-than-temporary impairment recorded	1,000,000	9,000,000
Impairment associated with adverse changes in timing of expected future cash flows	1,000,000	0
Impairment associated with expected credit losses	0	9,000,000
Gross pre-tax unrealized losses on securities	$ 442,000,000
Number of available for sale and held to maturity securities in gross pre-tax unrealized loss position	1,189