Preferred Stock Preferred Stock Summary (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Dec. 31, 2014
Class of Stock [Line Items]
Total shares issued and outstanding (shares)	15,826		15,826
Carrying value	$ 1,562	[1]	$ 1,562	[1]
Series A Preferred Stock
Class of Stock [Line Items]
Per annum dividend rate	Greater of (i) three-month LIBOR plus 0.565% for the related distribution period; or (ii) 4.000%
Per annum dividend rate (percent)	4.00%
Liquidation preference per share (usd per share)	$ 100,000
Total shares issued and outstanding (shares)	5,001		5,001
Carrying value	500	[1]	500	[1]
Series C Noncumulative Perpetual Preferred Stock
Class of Stock [Line Items]
Per annum dividend rate (percent)	5.20%
Liquidation preference per share (usd per share)	$ 100,000
Total shares issued and outstanding (shares)	5,825		5,825
Carrying value	568	[1]	568	[1]
Preferred stock redemption period following regulatory capital treatment event	90 days
Series D Preferred Stock
Class of Stock [Line Items]
Per annum dividend rate	4.50% commencing Dec. 20, 2013 to but excluding June 20, 2023, then a floating rate equal to the three-month LIBOR plus 2.46%
Per annum dividend rate (percent)	4.50%
Liquidation preference per share (usd per share)	$ 100,000
Total shares issued and outstanding (shares)	5,000		5,000
Carrying value	$ 494	[1]	$ 494	[1]
Preferred stock redemption period following regulatory capital treatment event	90 days
LIBOR | Series A Preferred Stock
Class of Stock [Line Items]
Preferred stock, basis spread on variable rate (percent)	0.565%
LIBOR | Series D Preferred Stock
Class of Stock [Line Items]
Preferred stock, basis spread on variable rate (percent)	2.46%

[1] The carrying value of the Series C and Series D preferred stock is recorded net of issuance costs.