Asset Quality - Aging Analysis of Past Due and Current Loans (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	$ 86,516	$ 84,716
Days Past Due	1,077	951
Non-performing Loans	545	503
Purchased Credit Impaired	629	738
Total loans	88,222	86,405
Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	64,063	61,904
Days Past Due	641	472
Non-performing Loans	243	191
Purchased Credit Impaired	272	357
Total loans		62,733
Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	22,453	22,812
Days Past Due	436	479
Non-performing Loans	302	312
Purchased Credit Impaired	357	381
Total loans		23,672
Commercial and Industrial [Member] | Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	44,137	41,444
Days Past Due	375	332
Non-performing Loans	178	153
Purchased Credit Impaired	57	83
Total loans	44,569	41,859
Commercial Real Estate: Commercial Mortgage [Member] | Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	13,740	13,750
Days Past Due	210	90
Non-performing Loans	42	30
Purchased Credit Impaired	212	248
Total loans	14,162	14,088
Commercial Real Estate: Construction [Member] | Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,719	1,919
Days Past Due	14	15
Non-performing Loans	2	2
Purchased Credit Impaired	3	26
Total loans	1,736	1,960
Commercial Real Estate Loans [Member] | Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	15,459	15,669
Days Past Due	224	105
Non-performing Loans	44	32
Purchased Credit Impaired	215	274
Total loans	15,898	16,048
Commercial Lease Financing [Member] | Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	4,467	4,791
Days Past Due	42	35
Non-performing Loans	21	6
Purchased Credit Impaired	0	0
Total loans	4,509	4,826
Commercial Loans [Member] | Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	64,976
Real Estate - Residential Mortgage [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	5,039	5,043
Days Past Due	80	85
Non-performing Loans	55	58
Purchased Credit Impaired	333	355
Total loans	5,452	5,483
Home Equity Loans [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	11,235	11,721
Days Past Due	264	285
Non-performing Loans	222	229
Purchased Credit Impaired	20	22
Total loans	11,519	12,028
Consumer Direct Loans [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,759	1,768
Days Past Due	22	22
Non-performing Loans	4	4
Purchased Credit Impaired	4	4
Total loans	1,785	1,794
Consumer Credit Card Financing Receivable [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,073	1,081
Days Past Due	21	25
Non-performing Loans	2	2
Purchased Credit Impaired	0	0
Total loans	1,094	1,106
Consumer Indirect Loans [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	3,347	3,199
Days Past Due	49	62
Non-performing Loans	19	19
Purchased Credit Impaired	0	0
Total loans	3,396	3,261
Consumer Portfolio Segment [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total loans	23,246
30-59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due	256	261
30-59 Days Past Due [Member] | Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due	184	164
30-59 Days Past Due [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due	72	97
30-59 Days Past Due [Member] | Commercial and Industrial [Member] | Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due	129	111
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	38	26
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	2	4
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	40	30
30-59 Days Past Due [Member] | Commercial Lease Financing [Member] | Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due	15	23
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	11	16
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	25	32
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	8	9
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	5	7
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	23	33
60-89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due	173	98
60-89 Days Past Due [Member] | Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due	143	60
60-89 Days Past Due [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due	30	38
60-89 Days Past Due [Member] | Commercial and Industrial [Member] | Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due	40	34
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	100	13
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	1	9
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	101	22
60-89 Days Past Due [Member] | Commercial Lease Financing [Member] | Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due	2	4
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	8	7
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	9	15
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	4
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	5	7
90 and Greater Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due	103	89
90 and Greater Days Past Due [Member] | Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due	71	57
90 and Greater Days Past Due [Member] | Consumer Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Days Past Due	32	32
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	28	34
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	30	21
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	9	0
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	39	21
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	4	2
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	6	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	8	9
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	6	5
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	10	11
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