Variable interest entities - Securitization Activity (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Residential mortgage | Level 2
All cash flows during the period:
Proceeds from new securitizations	$ 913,000,000	$ 484,000,000	$ 2,600,000,000	$ 1,100,000,000
Residential mortgage | Level 3
All cash flows during the period:
Proceeds from new securitizations	59,000,000	0	0	21,000,000
Commercial and other | Cash
All cash flows during the period:
Proceeds from new securitizations		0		280,000,000
Commercial and other | Level 2
All cash flows during the period:
Proceeds from new securitizations	3,000,000,000	3,100,000,000	9,000,000,000	7,400,000,000
Commercial and other | Level 3
All cash flows during the period:
Proceeds from new securitizations	5,000,000	0	43,000,000	130,000,000
Securitization entities not consolidated | Residential mortgage
Securitization activity [Abstract]
Principal securitized	971,000,000	484,000,000	2,663,000,000	1,144,000,000
All cash flows during the period:
Proceeds from new securitizations	972,000,000	484,000,000	2,674,000,000	1,147,000,000
Servicing fees collected	129,000,000	142,000,000	409,000,000	418,000,000
Purchases of previously transferred financial assets (or the underlying collateral)	1,000,000	52,000,000	2,000,000	119,000,000
Cash flows received on interests	122,000,000	43,000,000	308,000,000	128,000,000
Securitization entities not consolidated | Commercial and other
Securitization activity [Abstract]
Principal securitized	2,982,000,000	3,101,000,000	9,033,000,000	7,740,000,000
All cash flows during the period:
Proceeds from new securitizations	2,995,000,000	3,141,000,000	9,053,000,000	7,849,000,000
Servicing fees collected	0	1,000,000	2,000,000	3,000,000
Purchases of previously transferred financial assets (or the underlying collateral)	0	0	0	0
Cash flows received on interests	$ 172,000,000	$ 56,000,000	$ 379,000,000	$ 515,000,000