Loans and Allowance for Loan Losses (Details 2) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Financing Receivable, Allowance for Credit Losses
Allowance for loan losses, beginning of period	$ 536	$ 559	$ 537	$ 568
(Reversal of) provision for loan losses	(23)	18	(46)	25
Other	(1)		(2)	(1)
Loans charged-off	(15)	(18)	(46)	(39)
Recoveries of loans previously charged-off	4	6	12	26
Allowance for loan losses, end of period	547	529	547	529
Commercial portfolio
Financing Receivable, Allowance for Credit Losses
Allowance for loan losses, beginning of period	461	482	465	421
(Reversal of) provision for loan losses	(24)	15	(31)	(43)
Other	(1)		(2)	(1)
Loans charged-off	(11)	(15)	(28)	(29)
Recoveries of loans previously charged-off	3	5	10	23
Allowance for loan losses, end of period	476	457	476	457
Consumer portfolio
Financing Receivable, Allowance for Credit Losses
Allowance for loan losses, beginning of period	51	49	49	69
(Reversal of) provision for loan losses	1	(2)	(6)	13
Other	0		0	0
Loans charged-off	(1)	(2)	(7)	(9)
Recoveries of loans previously charged-off	1	0	2	2
Allowance for loan losses, end of period	50	49	50	49
Purchased credit-impaired loans
Financing Receivable, Allowance for Credit Losses
Allowance for loan losses, beginning of period	4	3	3	1
(Reversal of) provision for loan losses	0	0	(9)	(2)
Other	0		0	0
Loans charged-off	(3)	(1)	(11)	(1)
Recoveries of loans previously charged-off	0	1	0	1
Allowance for loan losses, end of period	1	3	1	3
Unallocated portfolio
Financing Receivable, Allowance for Credit Losses
Allowance for loan losses, beginning of period	20	25	20	77
(Reversal of) provision for loan losses	0	5	0	57
Other	0		0	0
Loans charged-off	0	0	0	0
Recoveries of loans previously charged-off	0	0	0	0
Allowance for loan losses, end of period	$ 20	$ 20	$ 20	$ 20