Asset Quality - Aging Analysis of Past Due and Current Loans (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable, Past Due [Line Items]
Current	$ 93,197	$ 88,011
Total Past Due and Non-performing Loans	1,003	966
Non-performing Loans	577	542
Purchased Credit Impaired	446	575
Total Loans	94,646	89,552
Financial Asset, 30 to 59 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Past Due and Non-performing Loans	228	218
Financial Asset, 60 to 89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Past Due and Non-performing Loans	101	94
Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Past Due and Non-performing Loans	97	112
Commercial Loans [Member]
Financing Receivable, Past Due [Line Items]
Current	67,224	65,558
Total Past Due and Non-performing Loans	635	511
Non-performing Loans	355	244
Purchased Credit Impaired	173	241
Total Loans	68,032	66,310
Commercial Loans [Member] | Commercial, Financial and Agricultural [Member]
Financing Receivable, Past Due [Line Items]
Current	47,768	45,375
Total Past Due and Non-performing Loans	479	317
Non-performing Loans	264	152
Purchased Credit Impaired	48	61
Total Loans	48,295	45,753
Commercial Loans [Member] | Commercial Real Estate: Commercial Mortgage [Member]
Financing Receivable, Past Due [Line Items]
Current	13,258	13,957
Total Past Due and Non-performing Loans	109	150
Non-performing Loans	83	81
Purchased Credit Impaired	124	178
Total Loans	13,491	14,285
Commercial Loans [Member] | Commercial Real Estate Construction [Member]
Financing Receivable, Past Due [Line Items]
Current	1,551	1,646
Total Past Due and Non-performing Loans	6	18
Non-performing Loans	2	2
Purchased Credit Impaired	1	2
Total Loans	1,558	1,666
Commercial Loans [Member] | Commercial Real Estate Loans [Member]
Financing Receivable, Past Due [Line Items]
Current	14,809	15,603
Total Past Due and Non-performing Loans	115	168
Non-performing Loans	85	83
Purchased Credit Impaired	125	180
Total Loans	15,049	15,951
Commercial Loans [Member] | Commercial Lease Financing [Member]
Financing Receivable, Past Due [Line Items]
Current	4,647	4,580
Total Past Due and Non-performing Loans	41	26
Non-performing Loans	6	9
Purchased Credit Impaired	0	0
Total Loans	4,688	4,606
Commercial Loans [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Past Due and Non-performing Loans	143	128
Commercial Loans [Member] | Financial Asset, 30 to 59 Days Past Due [Member] | Commercial, Financial and Agricultural [Member]
Financing Receivable, Past Due [Line Items]
Total Past Due and Non-performing Loans	110	89
Commercial Loans [Member] | Financial Asset, 30 to 59 Days Past Due [Member] | Commercial Real Estate: Commercial Mortgage [Member]
Financing Receivable, Past Due [Line Items]
Total Past Due and Non-performing Loans	8	27
Commercial Loans [Member] | Financial Asset, 30 to 59 Days Past Due [Member] | Commercial Real Estate Construction [Member]
Financing Receivable, Past Due [Line Items]
Total Past Due and Non-performing Loans	3	0
Commercial Loans [Member] | Financial Asset, 30 to 59 Days Past Due [Member] | Commercial Real Estate Loans [Member]
Financing Receivable, Past Due [Line Items]
Total Past Due and Non-performing Loans	11	27
Commercial Loans [Member] | Financial Asset, 30 to 59 Days Past Due [Member] | Commercial Lease Financing [Member]
Financing Receivable, Past Due [Line Items]
Total Past Due and Non-performing Loans	22	12
Commercial Loans [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Past Due and Non-performing Loans	68	62
Commercial Loans [Member] | Financial Asset, 60 to 89 Days Past Due [Member] | Commercial, Financial and Agricultural [Member]
Financing Receivable, Past Due [Line Items]
Total Past Due and Non-performing Loans	52	31
Commercial Loans [Member] | Financial Asset, 60 to 89 Days Past Due [Member] | Commercial Real Estate: Commercial Mortgage [Member]
Financing Receivable, Past Due [Line Items]
Total Past Due and Non-performing Loans	5	17
Commercial Loans [Member] | Financial Asset, 60 to 89 Days Past Due [Member] | Commercial Real Estate Construction [Member]
Financing Receivable, Past Due [Line Items]
Total Past Due and Non-performing Loans	0	13
Commercial Loans [Member] | Financial Asset, 60 to 89 Days Past Due [Member] | Commercial Real Estate Loans [Member]
Financing Receivable, Past Due [Line Items]
Total Past Due and Non-performing Loans	5	30
Commercial Loans [Member] | Financial Asset, 60 to 89 Days Past Due [Member] | Commercial Lease Financing [Member]
Financing Receivable, Past Due [Line Items]
Total Past Due and Non-performing Loans	11	1
Commercial Loans [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Past Due and Non-performing Loans	69	77
Commercial Loans [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Commercial, Financial and Agricultural [Member]
Financing Receivable, Past Due [Line Items]
Total Past Due and Non-performing Loans	53	45
Commercial Loans [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Commercial Real Estate: Commercial Mortgage [Member]
Financing Receivable, Past Due [Line Items]
Total Past Due and Non-performing Loans	13	25
Commercial Loans [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Commercial Real Estate Construction [Member]
Financing Receivable, Past Due [Line Items]
Total Past Due and Non-performing Loans	1	3
Commercial Loans [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Commercial Real Estate Loans [Member]
Financing Receivable, Past Due [Line Items]
Total Past Due and Non-performing Loans	14	28
Commercial Loans [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Commercial Lease Financing [Member]
Financing Receivable, Past Due [Line Items]
Total Past Due and Non-performing Loans	2	4
Consumer Loans [Member]
Financing Receivable, Past Due [Line Items]
Current	25,973	22,453
Total Past Due and Non-performing Loans	368	455
Non-performing Loans	222	298
Purchased Credit Impaired	273	334
Total Loans	26,614	23,242
Consumer Loans [Member] | Real Estate - Residential Mortgage [Member]
Financing Receivable, Past Due [Line Items]
Current	6,705	5,119
Total Past Due and Non-performing Loans	61	80
Non-performing Loans	48	62
Purchased Credit Impaired	257	314
Total Loans	7,023	5,513
Consumer Loans [Member] | Home Equity Loan [Member]
Financing Receivable, Past Due [Line Items]
Current	10,071	10,862
Total Past Due and Non-performing Loans	190	263
Non-performing Loans	145	210
Purchased Credit Impaired	13	17
Total Loans	10,274	11,142
Consumer Loans [Member] | Consumer Direct Loans [Member]
Financing Receivable, Past Due [Line Items]
Current	3,484	1,780
Total Past Due and Non-performing Loans	26	26
Non-performing Loans	4	4
Purchased Credit Impaired	3	3
Total Loans	3,513	1,809
Consumer Loans [Member] | Credit Card Receivable [Member]
Financing Receivable, Past Due [Line Items]
Current	1,104	1,119
Total Past Due and Non-performing Loans	26	25
Non-performing Loans	3	2
Purchased Credit Impaired	0	0
Total Loans	1,130	1,144
Consumer Loans [Member] | Consumer Indirect Loans [Member]
Financing Receivable, Past Due [Line Items]
Current	4,609	3,573
Total Past Due and Non-performing Loans	65	61
Non-performing Loans	22	20
Purchased Credit Impaired	0	0
Total Loans	4,674	3,634
Consumer Loans [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Past Due and Non-performing Loans	85	90
Consumer Loans [Member] | Financial Asset, 30 to 59 Days Past Due [Member] | Real Estate - Residential Mortgage [Member]
Financing Receivable, Past Due [Line Items]
Total Past Due and Non-performing Loans	7	11
Consumer Loans [Member] | Financial Asset, 30 to 59 Days Past Due [Member] | Home Equity Loan [Member]
Financing Receivable, Past Due [Line Items]
Total Past Due and Non-performing Loans	30	31
Consumer Loans [Member] | Financial Asset, 30 to 59 Days Past Due [Member] | Consumer Direct Loans [Member]
Financing Receivable, Past Due [Line Items]
Total Past Due and Non-performing Loans	10	11
Consumer Loans [Member] | Financial Asset, 30 to 59 Days Past Due [Member] | Credit Card Receivable [Member]
Financing Receivable, Past Due [Line Items]
Total Past Due and Non-performing Loans	6	6
Consumer Loans [Member] | Financial Asset, 30 to 59 Days Past Due [Member] | Consumer Indirect Loans [Member]
Financing Receivable, Past Due [Line Items]
Total Past Due and Non-performing Loans	32	31
Consumer Loans [Member] | Financial Asset, 60 to 89 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Past Due and Non-performing Loans	33	32
Consumer Loans [Member] | Financial Asset, 60 to 89 Days Past Due [Member] | Real Estate - Residential Mortgage [Member]
Financing Receivable, Past Due [Line Items]
Total Past Due and Non-performing Loans	5	3
Consumer Loans [Member] | Financial Asset, 60 to 89 Days Past Due [Member] | Home Equity Loan [Member]
Financing Receivable, Past Due [Line Items]
Total Past Due and Non-performing Loans	10	12
Consumer Loans [Member] | Financial Asset, 60 to 89 Days Past Due [Member] | Consumer Direct Loans [Member]
Financing Receivable, Past Due [Line Items]
Total Past Due and Non-performing Loans	5	5
Consumer Loans [Member] | Financial Asset, 60 to 89 Days Past Due [Member] | Credit Card Receivable [Member]
Financing Receivable, Past Due [Line Items]
Total Past Due and Non-performing Loans	5	5
Consumer Loans [Member] | Financial Asset, 60 to 89 Days Past Due [Member] | Consumer Indirect Loans [Member]
Financing Receivable, Past Due [Line Items]
Total Past Due and Non-performing Loans	8	7
Consumer Loans [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member]
Financing Receivable, Past Due [Line Items]
Total Past Due and Non-performing Loans	28	35
Consumer Loans [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Real Estate - Residential Mortgage [Member]
Financing Receivable, Past Due [Line Items]
Total Past Due and Non-performing Loans	1	4
Consumer Loans [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Home Equity Loan [Member]
Financing Receivable, Past Due [Line Items]
Total Past Due and Non-performing Loans	5	10
Consumer Loans [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Consumer Direct Loans [Member]
Financing Receivable, Past Due [Line Items]
Total Past Due and Non-performing Loans	7	6
Consumer Loans [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Credit Card Receivable [Member]
Financing Receivable, Past Due [Line Items]
Total Past Due and Non-performing Loans	12	12
Consumer Loans [Member] | Financial Asset, Equal to or Greater than 90 Days Past Due [Member] | Consumer Indirect Loans [Member]
Financing Receivable, Past Due [Line Items]
Total Past Due and Non-performing Loans	$ 3	$ 3