Preferred stock Preferred Stock Summary (Details) (USD $) In Millions, except Share data, unless otherwise specified	0 Months Ended	3 Months Ended		9 Months Ended
	Sep. 22, 2014	Sep. 30, 2014		Sep. 30, 2014		Dec. 31, 2013
Class of Stock [Line Items]
Total shares issued and outstanding (shares)		15,826		15,826		15,826
Carrying value		$ 1,562	[1]	$ 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%
Dividends Payable, Date of Record		Sep. 05, 2014
Preferred Stock Dividend Payment Date		Sep. 22, 2014
Liquidation preference per share (usd per share)		$ 100,000		$ 100,000
Total shares issued and outstanding (shares)		5,001		5,001		5,001
Carrying value		500	[1]	500	[1]	500	[1]
Depository share, value of preferred stock (percent)		1.00%		1.00%
Dividend paid per share (usd per share)	$ 1,044.44
Series C Noncumulative Perpetual Preferred Stock
Class of Stock [Line Items]
Per annum dividend rate (percent)				5.20%
Preferred stock redemption period following regulatory capital treatment event				90 days
Dividends Payable, Date of Record		Sep. 05, 2014
Preferred Stock Dividend Payment Date		Sep. 22, 2014
Liquidation preference per share (usd per share)		$ 100,000		$ 100,000
Total shares issued and outstanding (shares)		5,825		5,825		5,825
Carrying value		568	[1]	568	[1]	568	[1]
Depository share, value of preferred stock (percent)		0.025%		0.025%
Dividend paid per share (usd per share)	$ 1,300.00
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%
Preferred stock redemption period following regulatory capital treatment event				90 days
Liquidation preference per share (usd per share)		$ 100,000		$ 100,000
Total shares issued and outstanding (shares)		5,000		5,000		5,000
Carrying value		$ 494	[1]	$ 494	[1]	$ 494	[1]
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.