Asset Quality - Financing Receivable Credit Quality Indicators (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 89,268	$ 86,405
Consumer Portfolio Segment, PCI [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	345	381
Consumer Portfolio Segment, PCI [Member] | Residential Prime Financing Receivables [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	342	377
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 Credit Card [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 Excluding PCI [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	22,951	23,291
Consumer Portfolio Segment Excluding PCI [Member] | Residential Prime Financing Receivables [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	16,494	17,134
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Direct Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,804	1,790
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Credit Card [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,098	1,106
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Indirect Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,555	3,261
Commercial Portfolio Segment Excluding PCI Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	65,711	62,376
Commercial Portfolio Segment Excluding PCI Loans [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	63,152	59,785
Commercial Portfolio Segment Excluding PCI Loans [Member] | Criticized (Accruing) [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,223	2,400
Commercial Portfolio Segment Excluding PCI Loans [Member] | Criticized (Nonaccruing) [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	336	191
Commercial Portfolio Segment Excluding PCI Loans [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	44,969	41,776
Commercial Portfolio Segment Excluding PCI Loans [Member] | Commercial and Industrial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	43,052	39,833
Commercial Portfolio Segment Excluding PCI Loans [Member] | Commercial and Industrial [Member] | Criticized (Accruing) [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,691	1,790
Commercial Portfolio Segment Excluding PCI Loans [Member] | Commercial and Industrial [Member] | Criticized (Nonaccruing) [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	226	153
Commercial Portfolio Segment Excluding PCI Loans [Member] | RE Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	14,512	13,840
Commercial Portfolio Segment Excluding PCI Loans [Member] | RE Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	14,016	13,328
Commercial Portfolio Segment Excluding PCI Loans [Member] | RE Commercial [Member] | Criticized (Accruing) [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	398	482
Commercial Portfolio Segment Excluding PCI Loans [Member] | RE Commercial [Member] | Criticized (Nonaccruing) [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	98	30
Commercial Portfolio Segment Excluding PCI Loans [Member] | RE Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,760	1,934
Commercial Portfolio Segment Excluding PCI Loans [Member] | RE Construction [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,679	1,894
Commercial Portfolio Segment Excluding PCI Loans [Member] | RE Construction [Member] | Criticized (Accruing) [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	79	38
Commercial Portfolio Segment Excluding PCI Loans [Member] | RE Construction [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	4,470	4,826
Commercial Portfolio Segment Excluding PCI Loans [Member] | Commercial Leases [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,405	4,730
Commercial Portfolio Segment Excluding PCI Loans [Member] | Commercial Leases [Member] | Criticized (Accruing) [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	55	90
Commercial Portfolio Segment Excluding PCI Loans [Member] | Commercial Leases [Member] | Criticized (Nonaccruing) [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	10	6
Commercial Portfolio Segment, PCI [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	261	357
Commercial Portfolio Segment, PCI [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	160	220
Commercial Portfolio Segment, PCI [Member] | Criticized (Accruing) [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	101	137
Commercial Portfolio Segment, PCI [Member] | Commercial and Industrial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	54	83
Commercial Portfolio Segment, PCI [Member] | Commercial and Industrial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	23	41
Commercial Portfolio Segment, PCI [Member] | Commercial and Industrial [Member] | Criticized (Accruing) [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	31	42
Commercial Portfolio Segment, PCI [Member] | RE Commercial [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	204	248
Commercial Portfolio Segment, PCI [Member] | RE Commercial [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	134	153
Commercial Portfolio Segment, PCI [Member] | RE Commercial [Member] | Criticized (Accruing) [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	70	95
Commercial Portfolio Segment, PCI [Member] | RE Construction [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	3	26
Commercial Portfolio Segment, PCI [Member] | RE Construction [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	3	26
Commercial Portfolio Segment, PCI [Member] | RE Construction [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
FICO Score, 750 and Above [Member] | Consumer Portfolio Segment, PCI [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	138	149
FICO Score, 750 and Above [Member] | Consumer Portfolio Segment, PCI [Member] | Residential Prime Financing Receivables [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	138	149
FICO Score, 750 and Above [Member] | Consumer Portfolio Segment, PCI [Member] | Consumer Direct Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
FICO Score, 750 and Above [Member] | Consumer Portfolio Segment, PCI [Member] | Consumer Credit Card [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
FICO Score, 750 and Above [Member] | Consumer Portfolio Segment, PCI [Member] | Consumer Indirect Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
FICO Score, 750 and Above [Member] | Consumer Portfolio Segment Excluding PCI [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	12,696	12,694
FICO Score, 750 and Above [Member] | Consumer Portfolio Segment Excluding PCI [Member] | Residential Prime Financing Receivables [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	10,040	10,226
FICO Score, 750 and Above [Member] | Consumer Portfolio Segment Excluding PCI [Member] | Consumer Direct Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	551	519
FICO Score, 750 and Above [Member] | Consumer Portfolio Segment Excluding PCI [Member] | Consumer Credit Card [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	485	477
FICO Score, 750 and Above [Member] | Consumer Portfolio Segment Excluding PCI [Member] | Consumer Indirect Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,620	1,472
FICO Score, 660 to 749 [Member] | Consumer Portfolio Segment, PCI [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	98	119
FICO Score, 660 to 749 [Member] | Consumer Portfolio Segment, PCI [Member] | Residential Prime Financing Receivables [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	97	117
FICO Score, 660 to 749 [Member] | Consumer Portfolio Segment, PCI [Member] | Consumer Direct Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1	2
FICO Score, 660 to 749 [Member] | Consumer Portfolio Segment, PCI [Member] | Consumer Credit Card [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
FICO Score, 660 to 749 [Member] | Consumer Portfolio Segment, PCI [Member] | Consumer Indirect Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
FICO Score, 660 to 749 [Member] | Consumer Portfolio Segment Excluding PCI [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	7,367	7,563
FICO Score, 660 to 749 [Member] | Consumer Portfolio Segment Excluding PCI [Member] | Residential Prime Financing Receivables [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,850	5,181
FICO Score, 660 to 749 [Member] | Consumer Portfolio Segment Excluding PCI [Member] | Consumer Direct Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	701	690
FICO Score, 660 to 749 [Member] | Consumer Portfolio Segment Excluding PCI [Member] | Consumer Credit Card [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	501	508
FICO Score, 660 to 749 [Member] | Consumer Portfolio Segment Excluding PCI [Member] | Consumer Indirect Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,315	1,184
FICO Score, Less than 660 [Member] | Consumer Portfolio Segment, PCI [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	101	107
FICO Score, Less than 660 [Member] | Consumer Portfolio Segment, PCI [Member] | Residential Prime Financing Receivables [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	99	105
FICO Score, Less than 660 [Member] | Consumer Portfolio Segment, PCI [Member] | Consumer Direct Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2	2
FICO Score, Less than 660 [Member] | Consumer Portfolio Segment, PCI [Member] | Consumer Credit Card [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
FICO Score, Less than 660 [Member] | Consumer Portfolio Segment, PCI [Member] | Consumer Indirect Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
FICO Score, Less than 660 [Member] | Consumer Portfolio Segment Excluding PCI [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,221	2,394
FICO Score, Less than 660 [Member] | Consumer Portfolio Segment Excluding PCI [Member] | Residential Prime Financing Receivables [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,384	1,519
FICO Score, Less than 660 [Member] | Consumer Portfolio Segment Excluding PCI [Member] | Consumer Direct Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	211	225
FICO Score, Less than 660 [Member] | Consumer Portfolio Segment Excluding PCI [Member] | Consumer Credit Card [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	112	121
FICO Score, Less than 660 [Member] | Consumer Portfolio Segment Excluding PCI [Member] | Consumer Indirect Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	514	529
FICO Score, No Score [Member] | Consumer Portfolio Segment, PCI [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	8	6
FICO Score, No Score [Member] | Consumer Portfolio Segment, PCI [Member] | Residential Prime Financing Receivables [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	8	6
FICO Score, No Score [Member] | Consumer Portfolio Segment, PCI [Member] | Consumer Direct Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
FICO Score, No Score [Member] | Consumer Portfolio Segment, PCI [Member] | Consumer Credit Card [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
FICO Score, No Score [Member] | Consumer Portfolio Segment, PCI [Member] | Consumer Indirect Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
FICO Score, No Score [Member] | Consumer Portfolio Segment Excluding PCI [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	667	640
FICO Score, No Score [Member] | Consumer Portfolio Segment Excluding PCI [Member] | Residential Prime Financing Receivables [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	220	208
FICO Score, No Score [Member] | Consumer Portfolio Segment Excluding PCI [Member] | Consumer Direct Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	341	356
FICO Score, No Score [Member] | Consumer Portfolio Segment Excluding PCI [Member] | Consumer Credit Card [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	0
FICO Score, No Score [Member] | Consumer Portfolio Segment Excluding PCI [Member] | Consumer Indirect Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 106	$ 76