Asset Quality - Aging Analysis of Past Due and Current Loans (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	$ 88,671	$ 88,011
Days Past Due	956	966
Non-performing Loans	548	542
Purchased Credit Impaired	551	575
Total loans	90,178	89,552
Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	65,986	65,558
Days Past Due	528	511
Non-performing Loans	263	244
Purchased Credit Impaired	231	241
Total loans	66,745	66,310
Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	22,685	22,453
Days Past Due	428	455
Non-performing Loans	285	298
Purchased Credit Impaired	320	334
Total loans	23,433	23,242
Commercial and Industrial [Member] | Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	46,063	45,375
Days Past Due	353	317
Non-performing Loans	170	152
Purchased Credit Impaired	58	61
Total loans	46,474	45,753
Commercial Real Estate: Commercial Mortgage [Member] | Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	14,056	13,957
Days Past Due	116	150
Non-performing Loans	82	81
Purchased Credit Impaired	172	178
Total loans	14,344	14,285
Commercial Real Estate: Construction [Member] | Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,404	1,646
Days Past Due	15	18
Non-performing Loans	2	2
Purchased Credit Impaired	1	2
Total loans	1,420	1,666
Commercial Real Estate Loans [Member] | Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	15,460	15,603
Days Past Due	131	168
Non-performing Loans	84	83
Purchased Credit Impaired	173	180
Total loans	15,764	15,951
Commercial Lease Financing [Member] | Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	4,463	4,580
Days Past Due	44	26
Non-performing Loans	9	9
Purchased Credit Impaired	0	0
Total loans	4,507	4,606
Real Estate - Residential Mortgage [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	5,234	5,119
Days Past Due	80	80
Non-performing Loans	64	62
Purchased Credit Impaired	301	314
Total loans	5,615	5,513
Home Equity Loans [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	10,583	10,862
Days Past Due	247	263
Non-performing Loans	195	210
Purchased Credit Impaired	16	17
Total loans	10,846	11,142
Consumer Direct Loans [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	2,141	1,780
Days Past Due	21	26
Non-performing Loans	3	4
Purchased Credit Impaired	3	3
Total loans	2,165	1,809
Consumer Credit Card Financing Receivable [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,061	1,119
Days Past Due	25	25
Non-performing Loans	3	2
Purchased Credit Impaired	0	0
Total loans	1,086	1,144
Consumer Indirect Loans [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	3,666	3,573
Days Past Due	55	61
Non-performing Loans	20	20
Purchased Credit Impaired	0	0
Total loans	3,721	3,634
30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due	193	218
30-59 Days Past Due [Member] | Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due	113	128
30-59 Days Past Due [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due	80	90
30-59 Days Past Due [Member] | Commercial and Industrial [Member] | Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due	79	89
30-59 Days Past Due [Member] | Commercial Real Estate: Commercial Mortgage [Member] | Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due	10	27
30-59 Days Past Due [Member] | Commercial Real Estate: Construction [Member] | Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due	6	0
30-59 Days Past Due [Member] | Commercial Real Estate Loans [Member] | Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due	16	27
30-59 Days Past Due [Member] | Commercial Lease Financing [Member] | Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due	18	12
30-59 Days Past Due [Member] | Real Estate - Residential Mortgage [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due	9	11
30-59 Days Past Due [Member] | Home Equity Loans [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due	31	31
30-59 Days Past Due [Member] | Consumer Direct Loans [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due	7	11
30-59 Days Past Due [Member] | Consumer Credit Card Financing Receivable [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due	7	6
30-59 Days Past Due [Member] | Consumer Indirect Loans [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due	26	31
60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due	97	94
60-89 Days Past Due [Member] | Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due	66	62
60-89 Days Past Due [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due	31	32
60-89 Days Past Due [Member] | Commercial and Industrial [Member] | Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due	47	31
60-89 Days Past Due [Member] | Commercial Real Estate: Commercial Mortgage [Member] | Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due	7	17
60-89 Days Past Due [Member] | Commercial Real Estate: Construction [Member] | Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due	0	13
60-89 Days Past Due [Member] | Commercial Real Estate Loans [Member] | Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due	7	30
60-89 Days Past Due [Member] | Commercial Lease Financing [Member] | Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due	12	1
60-89 Days Past Due [Member] | Real Estate - Residential Mortgage [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due	4	3
60-89 Days Past Due [Member] | Home Equity Loans [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due	12	12
60-89 Days Past Due [Member] | Consumer Direct Loans [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due	4	5
60-89 Days Past Due [Member] | Consumer Credit Card Financing Receivable [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due	4	5
60-89 Days Past Due [Member] | Consumer Indirect Loans [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due	7	7
90 and Greater Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due	118	112
90 and Greater Days Past Due [Member] | Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due	86	77
90 and Greater Days Past Due [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due	32	35
90 and Greater Days Past Due [Member] | Commercial and Industrial [Member] | Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due	57	45
90 and Greater Days Past Due [Member] | Commercial Real Estate: Commercial Mortgage [Member] | Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due	17	25
90 and Greater Days Past Due [Member] | Commercial Real Estate: Construction [Member] | Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due	7	3
90 and Greater Days Past Due [Member] | Commercial Real Estate Loans [Member] | Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due	24	28
90 and Greater Days Past Due [Member] | Commercial Lease Financing [Member] | Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due	5	4
90 and Greater Days Past Due [Member] | Real Estate - Residential Mortgage [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due	3	4
90 and Greater Days Past Due [Member] | Home Equity Loans [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due	9	10
90 and Greater Days Past Due [Member] | Consumer Direct Loans [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due	7	6
90 and Greater Days Past Due [Member] | Consumer Credit Card Financing Receivable [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due	11	12
90 and Greater Days Past Due [Member] | Consumer Indirect Loans [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due	$ 2	$ 3