Loans - Wholesale Loan Portfolio - Impaired Loans (Details) (Wholesale, USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Commercial and industrial
Impaired loans:
With an allowance	$ 174	$ 236
Without an allowance	24	58
Total impaired loans	198	294
Allowance for loan losses related to impaired loans	34	75
Unpaid principal balance of impaired loans	266	448
Average impaired loans	243	412	873
Real estate
Impaired loans:
With an allowance	193	258
Without an allowance	87	109
Total impaired loans	280	367
Allowance for loan losses related to impaired loans	36	63
Unpaid principal balance of impaired loans	345	454
Average impaired loans	297	484	784
Financial institutions
Impaired loans:
With an allowance	15	17
Without an allowance	3	8
Total impaired loans	18	25
Allowance for loan losses related to impaired loans	4	16
Unpaid principal balance of impaired loans	22	24
Average impaired loans	20	17	17
Government agencies
Impaired loans:
With an allowance	0	1
Without an allowance	0	0
Total impaired loans	0	1
Allowance for loan losses related to impaired loans	0	0
Unpaid principal balance of impaired loans	0	1
Average impaired loans	0	0	9
Other
Impaired loans:
With an allowance	89	85
Without an allowance	52	73
Total impaired loans	141	158
Allowance for loan losses related to impaired loans	13	27
Unpaid principal balance of impaired loans	202	241
Average impaired loans	155	211	277
Commercial loan
Impaired loans:
With an allowance	471	597
Without an allowance	166	248
Total impaired loans	637	845
Allowance for loan losses related to impaired loans	87	181
Unpaid principal balance of impaired loans	835	1,168
Average impaired loans	$ 715	$ 1,124	$ 1,960