Asset Quality - Financing Receivable Credit Quality Indicators (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Total loans	$ 86,405	$ 86,038
Commercial Portfolio Segment Excluding PCI Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	62,376	61,449
Commercial Portfolio Segment Excluding PCI Loans [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	59,785	59,072
Commercial Portfolio Segment Excluding PCI Loans [Member] | Criticized Accruing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,400	2,044
Commercial Portfolio Segment Excluding PCI Loans [Member] | Criticized Nonaccruing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	191	333
Commercial Portfolio Segment Excluding PCI Loans [Member] | Commercial, Financial and Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	41,776	39,656
Commercial Portfolio Segment Excluding PCI Loans [Member] | Commercial, Financial and Agricultural [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	39,833	37,845
Commercial Portfolio Segment Excluding PCI Loans [Member] | Commercial, Financial and Agricultural [Member] | Criticized Accruing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,790	1,514
Commercial Portfolio Segment Excluding PCI Loans [Member] | Commercial, Financial and Agricultural [Member] | Criticized Nonaccruing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	153	297
Commercial Portfolio Segment Excluding PCI Loans [Member] | Commercial Real Estate Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	13,840	14,789
Commercial Portfolio Segment Excluding PCI Loans [Member] | Commercial Real Estate Loans [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	13,328	14,308
Commercial Portfolio Segment Excluding PCI Loans [Member] | Commercial Real Estate Loans [Member] | Criticized Accruing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	482	455
Commercial Portfolio Segment Excluding PCI Loans [Member] | Commercial Real Estate Loans [Member] | Criticized Nonaccruing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	30	26
Commercial Portfolio Segment Excluding PCI Loans [Member] | Construction Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,934	2,319
Commercial Portfolio Segment Excluding PCI Loans [Member] | Construction Loans [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,894	2,287
Commercial Portfolio Segment Excluding PCI Loans [Member] | Construction Loans [Member] | Criticized Accruing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	38	30
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	4,826	4,685
Commercial Portfolio Segment Excluding PCI Loans [Member] | Commercial Leases [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	4,730	4,632
Commercial Portfolio Segment Excluding PCI Loans [Member] | Commercial Leases [Member] | Criticized Accruing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	90	45
Commercial Portfolio Segment Excluding PCI Loans [Member] | Commercial Leases [Member] | Criticized Nonaccruing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	6	8
Consumer Portfolio Segment Excluding PCI [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	23,291	23,724
Consumer Portfolio Segment Excluding PCI [Member] | FICO Score, 750 and Above [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	12,694	12,035
Consumer Portfolio Segment Excluding PCI [Member] | FICO Score, 660 to 749 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	7,563	7,647
Consumer Portfolio Segment Excluding PCI [Member] | FICO Score, Less than 660 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	2,394	2,486
Consumer Portfolio Segment Excluding PCI [Member] | FICO Score, No Score [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	640	1,556
Consumer Portfolio Segment Excluding PCI [Member] | Residential Prime Financing Receivables [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	17,134	17,823
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	10,226	9,818
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	5,181	5,266
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	1,519	1,617
Consumer Portfolio Segment Excluding PCI [Member] | Residential Prime Financing Receivables [Member] | FICO Score, No Score [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	208	1,122
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Direct Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,790	1,781
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Direct Loans [Member] | FICO Score, 750 and Above [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	519	498
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Direct Loans [Member] | FICO Score, 660 to 749 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	690	661
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Direct Loans [Member] | FICO Score, Less than 660 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	225	194
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Direct Loans [Member] | FICO Score, No Score [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	356	428
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Credit Card [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,106	1,111
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Credit Card [Member] | FICO Score, 750 and Above [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	477	453
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Credit Card [Member] | FICO Score, 660 to 749 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	508	525
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Credit Card [Member] | FICO Score, Less than 660 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	121	132
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Credit Card [Member] | FICO Score, No Score [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	1
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Indirect Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	3,261	3,009
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Indirect Loans [Member] | FICO Score, 750 and Above [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,472	1,266
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Indirect Loans [Member] | FICO Score, 660 to 749 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	1,184	1,195
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Indirect Loans [Member] | FICO Score, Less than 660 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	529	543
Consumer Portfolio Segment Excluding PCI [Member] | Consumer Indirect Loans [Member] | FICO Score, No Score [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	76	5
Commercial Portfolio Segment, PCI [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	357	460
Commercial Portfolio Segment, PCI [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	220	172
Commercial Portfolio Segment, PCI [Member] | Criticized Accruing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	137	288
Commercial Portfolio Segment, PCI [Member] | Commercial, Financial and Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	83	112
Commercial Portfolio Segment, PCI [Member] | Commercial, Financial and Agricultural [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	41	12
Commercial Portfolio Segment, PCI [Member] | Commercial, Financial and Agricultural [Member] | Criticized Accruing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	42	100
Commercial Portfolio Segment, PCI [Member] | Commercial Real Estate Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	248	322
Commercial Portfolio Segment, PCI [Member] | Commercial Real Estate Loans [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	153	139
Commercial Portfolio Segment, PCI [Member] | Commercial Real Estate Loans [Member] | Criticized Accruing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	95	183
Commercial Portfolio Segment, PCI [Member] | Construction Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	26	26
Commercial Portfolio Segment, PCI [Member] | Construction Loans [Member] | Pass [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	26	21
Commercial Portfolio Segment, PCI [Member] | Construction Loans [Member] | Criticized Accruing [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	5
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	381	405
Consumer Portfolio Segment, PCI [Member] | FICO Score, 750 and Above [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	149	133
Consumer Portfolio Segment, PCI [Member] | FICO Score, 660 to 749 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	119	129
Consumer Portfolio Segment, PCI [Member] | FICO Score, Less than 660 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	107	137
Consumer Portfolio Segment, PCI [Member] | FICO Score, No Score [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	6	6
Consumer Portfolio Segment, PCI [Member] | Residential Prime Financing Receivables [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	377	398
Consumer Portfolio Segment, PCI [Member] | Residential Prime Financing Receivables [Member] | FICO Score, 750 and Above [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	149	133
Consumer Portfolio Segment, PCI [Member] | Residential Prime Financing Receivables [Member] | FICO Score, 660 to 749 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	117	127
Consumer Portfolio Segment, PCI [Member] | Residential Prime Financing Receivables [Member] | FICO Score, Less than 660 [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	105	133
Consumer Portfolio Segment, PCI [Member] | Residential Prime Financing Receivables [Member] | FICO Score, No Score [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	6	5
Consumer Portfolio Segment, PCI [Member] | Consumer Direct Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	4	7
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	2	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	4
Consumer Portfolio Segment, PCI [Member] | Consumer Direct Loans [Member] | FICO Score, No Score [Member]
Financing Receivable, Recorded Investment [Line Items]
Total loans	0	1
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