Asset Quality - Aging Analysis of Past Due and Current Loans (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	$ 88,011	$ 84,716
Total Past Due and Non-performing Loans	966	951
Non-performing Loans	542	503
Purchased Credit Impaired	575	738
Total Loans	89,552	86,405
Financing Receivables, 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	218	261
Financing Receivables, 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	94	98
Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	112	89
Commercial Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	65,558	61,904
Total Past Due and Non-performing Loans	511	472
Non-performing Loans	244	191
Purchased Credit Impaired	241	357
Total Loans	66,310	62,733
Commercial Loans [Member] | Commercial, Financial and Agricultural [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	45,375	41,444
Total Past Due and Non-performing Loans	317	332
Non-performing Loans	152	153
Purchased Credit Impaired	61	83
Total Loans	45,753	41,859
Commercial Loans [Member] | Commercial Real Estate: Commercial Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	13,957	13,750
Total Past Due and Non-performing Loans	150	90
Non-performing Loans	81	30
Purchased Credit Impaired	178	248
Total Loans	14,285	14,088
Commercial Loans [Member] | Commercial Real Estate Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,646	1,919
Total Past Due and Non-performing Loans	18	15
Non-performing Loans	2	2
Purchased Credit Impaired	2	26
Total Loans	1,666	1,960
Commercial Loans [Member] | Commercial Real Estate Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	15,603	15,669
Total Past Due and Non-performing Loans	168	105
Non-performing Loans	83	32
Purchased Credit Impaired	180	274
Total Loans	15,951	16,048
Commercial Loans [Member] | Commercial Lease Financing [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	4,580	4,791
Total Past Due and Non-performing Loans	26	35
Non-performing Loans	9	6
Purchased Credit Impaired	0	0
Total Loans	4,606	4,826
Commercial Loans [Member] | Financing Receivables, 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	128	164
Commercial Loans [Member] | Financing Receivables, 30 to 59 Days Past Due [Member] | Commercial, Financial and Agricultural [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	89	111
Commercial Loans [Member] | Financing Receivables, 30 to 59 Days Past Due [Member] | Commercial Real Estate: Commercial Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	27	26
Commercial Loans [Member] | Financing Receivables, 30 to 59 Days Past Due [Member] | Commercial Real Estate Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	0	4
Commercial Loans [Member] | Financing Receivables, 30 to 59 Days Past Due [Member] | Commercial Real Estate Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	27	30
Commercial Loans [Member] | Financing Receivables, 30 to 59 Days Past Due [Member] | Commercial Lease Financing [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	12	23
Commercial Loans [Member] | Financing Receivables, 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	62	60
Commercial Loans [Member] | Financing Receivables, 60 to 89 Days Past Due [Member] | Commercial, Financial and Agricultural [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	31	34
Commercial Loans [Member] | Financing Receivables, 60 to 89 Days Past Due [Member] | Commercial Real Estate: Commercial Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	17	13
Commercial Loans [Member] | Financing Receivables, 60 to 89 Days Past Due [Member] | Commercial Real Estate Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	13	9
Commercial Loans [Member] | Financing Receivables, 60 to 89 Days Past Due [Member] | Commercial Real Estate Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	30	22
Commercial Loans [Member] | Financing Receivables, 60 to 89 Days Past Due [Member] | Commercial Lease Financing [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	1	4
Commercial Loans [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	77	57
Commercial Loans [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Commercial, Financial and Agricultural [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	45	34
Commercial Loans [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Commercial Real Estate: Commercial Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	25	21
Commercial Loans [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Commercial Real Estate Construction [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	3	0
Commercial Loans [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Commercial Real Estate Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	28	21
Commercial Loans [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Commercial Lease Financing [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	4	2
Consumer Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	22,453	22,812
Total Past Due and Non-performing Loans	455	479
Non-performing Loans	298	312
Purchased Credit Impaired	334	381
Total Loans	23,242	23,672
Consumer Loans [Member] | Real Estate - Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	5,119	5,043
Total Past Due and Non-performing Loans	80	85
Non-performing Loans	62	58
Purchased Credit Impaired	314	355
Total Loans	5,513	5,483
Consumer Loans [Member] | Home Equity Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	10,862	11,721
Total Past Due and Non-performing Loans	263	285
Non-performing Loans	210	229
Purchased Credit Impaired	17	22
Total Loans	11,142	12,028
Consumer Loans [Member] | Consumer Direct Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,780	1,768
Total Past Due and Non-performing Loans	26	22
Non-performing Loans	4	4
Purchased Credit Impaired	3	4
Total Loans	1,809	1,794
Consumer Loans [Member] | Credit Card Receivable [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	1,119	1,081
Total Past Due and Non-performing Loans	25	25
Non-performing Loans	2	2
Purchased Credit Impaired	0	0
Total Loans	1,144	1,106
Consumer Loans [Member] | Consumer Indirect Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Current	3,573	3,199
Total Past Due and Non-performing Loans	61	62
Non-performing Loans	20	19
Purchased Credit Impaired	0	0
Total Loans	3,634	3,261
Consumer Loans [Member] | Financing Receivables, 30 to 59 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	90	97
Consumer Loans [Member] | Financing Receivables, 30 to 59 Days Past Due [Member] | Real Estate - Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	11	16
Consumer Loans [Member] | Financing Receivables, 30 to 59 Days Past Due [Member] | Home Equity Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	31	32
Consumer Loans [Member] | Financing Receivables, 30 to 59 Days Past Due [Member] | Consumer Direct Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	11	9
Consumer Loans [Member] | Financing Receivables, 30 to 59 Days Past Due [Member] | Credit Card Receivable [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	6	7
Consumer Loans [Member] | Financing Receivables, 30 to 59 Days Past Due [Member] | Consumer Indirect Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	31	33
Consumer Loans [Member] | Financing Receivables, 60 to 89 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	32	38
Consumer Loans [Member] | Financing Receivables, 60 to 89 Days Past Due [Member] | Real Estate - Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	3	7
Consumer Loans [Member] | Financing Receivables, 60 to 89 Days Past Due [Member] | Home Equity Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	12	15
Consumer Loans [Member] | Financing Receivables, 60 to 89 Days Past Due [Member] | Consumer Direct Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	5	4
Consumer Loans [Member] | Financing Receivables, 60 to 89 Days Past Due [Member] | Credit Card Receivable [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	5	5
Consumer Loans [Member] | Financing Receivables, 60 to 89 Days Past Due [Member] | Consumer Indirect Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	7	7
Consumer Loans [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	35	32
Consumer Loans [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Real Estate - Residential Mortgage [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	4	4
Consumer Loans [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Home Equity Loan [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	10	9
Consumer Loans [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Consumer Direct Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	6	5
Consumer Loans [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Credit Card Receivable [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	12	11
Consumer Loans [Member] | Financing Receivables, Equal to Greater than 90 Days Past Due [Member] | Consumer Indirect Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Past Due and Non-performing Loans	$ 3	$ 3