Loans and ACL (Aging Analysis of Past Due Loans and Leases) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Loans and leases, current	$ 133,668	$ 117,425
Loans and leases, 30-89 days past due	1,030	898
Loans and leases, 90 days or more past due	677	945
Nonaccrual loans and leases	576	616
Total loans and leases	135,951	119,884
Commercial and Industrial [Member]
Loans and leases, current	48,157	41,192
Loans and leases, 30-89 days past due	36	23
Loans and leases, 90 days or more past due	0	0
Nonaccrual loans and leases	237	239
Total loans and leases	48,430	41,454
CRE-Income Producing Properties [Member]
Loans and leases, current	13,370	10,644
Loans and leases, 30-89 days past due	13	4
Loans and leases, 90 days or more past due	0	0
Nonaccrual loans and leases	38	74
Total loans and leases	13,421	10,722
CRE-Construction And Development [Member]
Loans and leases, current	3,710	2,708
Loans and leases, 30-89 days past due	9	1
Loans and leases, 90 days or more past due	0	0
Nonaccrual loans and leases	13	26
Total loans and leases	3,732	2,735
Commercial Dealer Floor Plan [Member]
Loans and leases, current	1,215	1,091
Loans and leases, 30-89 days past due	0	0
Loans and leases, 90 days or more past due	0	0
Nonaccrual loans and leases	0	0
Total loans and leases	1,215	1,091
Commercial Other Lending Subsidiaries [Member]
Loans and leases, current	6,771	5,337
Loans and leases, 30-89 days past due	18	15
Loans and leases, 90 days or more past due	0	0
Nonaccrual loans and leases	6	4
Total loans and leases	6,795	5,356
Direct Retail Lending [Member]
Loans and leases, current	11,032	8,045
Loans and leases, 30-89 days past due	58	41
Loans and leases, 90 days or more past due	7	12
Nonaccrual loans and leases	43	48
Total loans and leases	11,140	8,146
Retail Revolving Credit [Member]
Loans and leases, current	2,478	2,428
Loans and leases, 30-89 days past due	22	23
Loans and leases, 90 days or more past due	10	9
Nonaccrual loans and leases	0	0
Total loans and leases	2,510	2,460
Retail Residential Mortgage-Nonguaranteed [Member]
Loans and leases, current	29,038	29,468
Loans and leases, 30-89 days past due	397	392
Loans and leases, 90 days or more past due	55	83
Nonaccrual loans and leases	173	164
Total loans and leases	29,663	30,107
Retail Residential Mortgage-Government Guaranteed [Member]
Loans and leases, current	307	251
Loans and leases, 30-89 days past due	77	82
Loans and leases, 90 days or more past due	486	648
Nonaccrual loans and leases	0	2
Total loans and leases	870	983
Retail Sales Finance [Member]
Loans and leases, current	10,243	9,437
Loans and leases, 30-89 days past due	72	62
Loans and leases, 90 days or more past due	5	5
Nonaccrual loans and leases	7	5
Total loans and leases	10,327	9,509
Retail Other Lending Subsidiaries [Member]
Loans and leases, current	6,381	5,830
Loans and leases, 30-89 days past due	286	222
Loans and leases, 90 days or more past due	0	0
Nonaccrual loans and leases	59	54
Total loans and leases	6,726	6,106
PCI [Member]
Loans and leases, current	966	994
Loans and leases, 30-89 days past due	42	33
Loans and leases, 90 days or more past due	114	188
Nonaccrual loans and leases	0	0
Total loans and leases	$ 1,122	$ 1,215