Loans - Wholesale Loan Portfolio - Impaired Loans (Details) - Wholesale - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Total retained loans
Impaired loans:
With an allowance	$ 726	$ 471
Without an allowance	298	166
Total impaired loans	1,024	637
Allowance for loan losses related to impaired loans	274	87
Unpaid principal balance of impaired loans	1,209	835
Average impaired loans	845	715	$ 1,124
Commercial and industrial
Impaired loans:
With an allowance	522	174
Without an allowance	98	24
Total impaired loans	620	198
Allowance for loan losses related to impaired loans	220	34
Unpaid principal balance of impaired loans	669	266
Average impaired loans	453	243	412
Real estate
Impaired loans:
With an allowance	148	193
Without an allowance	106	87
Total impaired loans	254	280
Allowance for loan losses related to impaired loans	27	36
Unpaid principal balance of impaired loans	363	345
Average impaired loans	250	297	484
Financial institutions
Impaired loans:
With an allowance	10	15
Without an allowance	0	3
Total impaired loans	10	18
Allowance for loan losses related to impaired loans	3	4
Unpaid principal balance of impaired loans	13	22
Average impaired loans	13	20	17
Government agencies
Impaired loans:
With an allowance	0	0
Without an allowance	0	0
Total impaired loans	0	0
Allowance for loan losses related to impaired loans	0	0
Unpaid principal balance of impaired loans	0	0
Average impaired loans	0	0	0
Other
Impaired loans:
With an allowance	46	89
Without an allowance	94	52
Total impaired loans	140	141
Allowance for loan losses related to impaired loans	24	13
Unpaid principal balance of impaired loans	164	202
Average impaired loans	$ 129	$ 155	$ 211