Asset Quality - Financing Receivable Credit Quality Indicators (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 89,552	$ 86,405
Commercial Portfolio Segment Excluding PCI Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	66,069	62,376
Commercial Portfolio Segment Excluding PCI Loans [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	63,904	59,785
Commercial Portfolio Segment Excluding PCI Loans [Member] | Criticized Accruing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,922	2,400
Commercial Portfolio Segment Excluding PCI Loans [Member] | Criticized Nonaccruing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	243	191
Commercial Portfolio Segment Excluding PCI Loans [Member] | Commercial, Financial and Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	45,692	41,776
Commercial Portfolio Segment Excluding PCI Loans [Member] | Commercial, Financial and Agricultural [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	44,138	39,833
Commercial Portfolio Segment Excluding PCI Loans [Member] | Commercial, Financial and Agricultural [Member] | Criticized Accruing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,402	1,790
Commercial Portfolio Segment Excluding PCI Loans [Member] | Commercial, Financial and Agricultural [Member] | Criticized Nonaccruing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	152	153
Commercial Portfolio Segment Excluding PCI Loans [Member] | Commercial Real Estate Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	14,107	13,840
Commercial Portfolio Segment Excluding PCI Loans [Member] | Commercial Real Estate Loans [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	13,672	13,328
Commercial Portfolio Segment Excluding PCI Loans [Member] | Commercial Real Estate Loans [Member] | Criticized Accruing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	354	482
Commercial Portfolio Segment Excluding PCI Loans [Member] | Commercial Real Estate Loans [Member] | Criticized Nonaccruing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	81	30
Commercial Portfolio Segment Excluding PCI Loans [Member] | Construction Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,664	1,934
Commercial Portfolio Segment Excluding PCI Loans [Member] | Construction Loans [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,537	1,894
Commercial Portfolio Segment Excluding PCI Loans [Member] | Construction Loans [Member] | Criticized Accruing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	125	38
Commercial Portfolio Segment Excluding PCI Loans [Member] | Construction Loans [Member] | Criticized Nonaccruing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2	2
Commercial Portfolio Segment Excluding PCI Loans [Member] | Commercial Leases [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,606	4,826
Commercial Portfolio Segment Excluding PCI Loans [Member] | Commercial Leases [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,557	4,730
Commercial Portfolio Segment Excluding PCI Loans [Member] | Commercial Leases [Member] | Criticized Accruing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	41	90
Commercial Portfolio Segment Excluding PCI Loans [Member] | Commercial Leases [Member] | Criticized Nonaccruing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	8	6
Consumer Portfolio Segment Excluding PCI [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	22,908	23,291
Consumer Portfolio Segment Excluding PCI [Member] | FICO Score, 750 and Above [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	12,511	12,694
Consumer Portfolio Segment Excluding PCI [Member] | FICO Score, 660 to 749 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	7,433	7,563
Consumer Portfolio Segment Excluding PCI [Member] | FICO Score, Less than 660 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,316	2,394
Consumer Portfolio Segment Excluding PCI [Member] | FICO Score, No Score [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	648	640
Consumer Portfolio Segment Excluding PCI [Member] | Residential Prime Financing Receivables [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	16,324	17,134
Consumer Portfolio Segment Excluding PCI [Member] | Residential Prime Financing Receivables [Member] | FICO Score, 750 and Above [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	9,794	10,226
Consumer Portfolio Segment Excluding PCI [Member] | Residential Prime Financing Receivables [Member] | FICO Score, 660 to 749 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,906	5,181
Consumer Portfolio Segment Excluding PCI [Member] | Residential Prime Financing Receivables [Member] | FICO Score, Less than 660 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,411	1,519
Consumer Portfolio Segment Excluding PCI [Member] | Residential Prime Financing Receivables [Member] | FICO Score, No Score [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	213	208
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Direct Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,806	1,790
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Direct Loans [Member] | FICO Score, 750 and Above [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	549	519
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Direct Loans [Member] | FICO Score, 660 to 749 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	700	690
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Direct Loans [Member] | FICO Score, Less than 660 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	224	225
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Direct Loans [Member] | FICO Score, No Score [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	333	356
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Credit Card [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,144	1,106
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Credit Card [Member] | FICO Score, 750 and Above [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	521	477
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Credit Card [Member] | FICO Score, 660 to 749 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	507	508
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Credit Card [Member] | FICO Score, Less than 660 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	116	121
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Credit Card [Member] | FICO Score, No Score [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Indirect Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,634	3,261
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Indirect Loans [Member] | FICO Score, 750 and Above [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,647	1,472
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Indirect Loans [Member] | FICO Score, 660 to 749 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,320	1,184
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Indirect Loans [Member] | FICO Score, Less than 660 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	565	529
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Indirect Loans [Member] | FICO Score, No Score [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	102	76
Commercial Portfolio Segment, PCI [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	241	357
Commercial Portfolio Segment, PCI [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	164	220
Commercial Portfolio Segment, PCI [Member] | Criticized Accruing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	77	137
Commercial Portfolio Segment, PCI [Member] | Commercial, Financial and Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	61	83
Commercial Portfolio Segment, PCI [Member] | Commercial, Financial and Agricultural [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	37	41
Commercial Portfolio Segment, PCI [Member] | Commercial, Financial and Agricultural [Member] | Criticized Accruing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	24	42
Commercial Portfolio Segment, PCI [Member] | Commercial Real Estate Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	178	248
Commercial Portfolio Segment, PCI [Member] | Commercial Real Estate Loans [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	125	153
Commercial Portfolio Segment, PCI [Member] | Commercial Real Estate Loans [Member] | Criticized Accruing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	53	95
Commercial Portfolio Segment, PCI [Member] | Construction Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2	26
Commercial Portfolio Segment, PCI [Member] | Construction Loans [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2	26
Commercial Portfolio Segment, PCI [Member] | Construction Loans [Member] | Criticized Accruing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Commercial Portfolio Segment, PCI [Member] | Commercial Leases [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Commercial Portfolio Segment, PCI [Member] | Commercial Leases [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Commercial Portfolio Segment, PCI [Member] | Commercial Leases [Member] | Criticized Accruing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Consumer Portfolio Segment, PCI [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	334	381
Consumer Portfolio Segment, PCI [Member] | FICO Score, 750 and Above [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	137	149
Consumer Portfolio Segment, PCI [Member] | FICO Score, 660 to 749 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	96	119
Consumer Portfolio Segment, PCI [Member] | FICO Score, Less than 660 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	99	107
Consumer Portfolio Segment, PCI [Member] | FICO Score, No Score [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2	6
Consumer Portfolio Segment, PCI [Member] | Residential Prime Financing Receivables [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	331	377
Consumer Portfolio Segment, PCI [Member] | Residential Prime Financing Receivables [Member] | FICO Score, 750 and Above [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	137	149
Consumer Portfolio Segment, PCI [Member] | Residential Prime Financing Receivables [Member] | FICO Score, 660 to 749 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	95	117
Consumer Portfolio Segment, PCI [Member] | Residential Prime Financing Receivables [Member] | FICO Score, Less than 660 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	97	105
Consumer Portfolio Segment, PCI [Member] | Residential Prime Financing Receivables [Member] | FICO Score, No Score [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2	6
Consumer Portfolio Segment, PCI [Member] | Consumer Direct Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	3	4
Consumer Portfolio Segment, PCI [Member] | Consumer Direct Loans [Member] | FICO Score, 750 and Above [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Consumer Portfolio Segment, PCI [Member] | Consumer Direct Loans [Member] | FICO Score, 660 to 749 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1	2
Consumer Portfolio Segment, PCI [Member] | Consumer Direct Loans [Member] | FICO Score, Less than 660 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2	2
Consumer Portfolio Segment, PCI [Member] | Consumer Direct Loans [Member] | FICO Score, No Score [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Consumer Portfolio Segment, PCI [Member] | Consumer Credit Card [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Consumer Portfolio Segment, PCI [Member] | Consumer Credit Card [Member] | FICO Score, 750 and Above [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Consumer Portfolio Segment, PCI [Member] | Consumer Credit Card [Member] | FICO Score, 660 to 749 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Consumer Portfolio Segment, PCI [Member] | Consumer Credit Card [Member] | FICO Score, Less than 660 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Consumer Portfolio Segment, PCI [Member] | Consumer Credit Card [Member] | FICO Score, No Score [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Consumer Portfolio Segment, PCI [Member] | Consumer Indirect Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Consumer Portfolio Segment, PCI [Member] | Consumer Indirect Loans [Member] | FICO Score, 750 and Above [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Consumer Portfolio Segment, PCI [Member] | Consumer Indirect Loans [Member] | FICO Score, 660 to 749 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Consumer Portfolio Segment, PCI [Member] | Consumer Indirect Loans [Member] | FICO Score, Less than 660 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
Consumer Portfolio Segment, PCI [Member] | Consumer Indirect Loans [Member] | FICO Score, No Score [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 0	$ 0