Asset Quality - Commercial Credit Exposure (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
Total	$ 103,081	$ 94,646
Accrued interest	235	244
Commercial Loans
Financing Receivable, Credit Quality Indicator [Line Items]
2020	15,761
2019	11,206
2018	7,966
2017	5,215
2016	3,705
Prior	7,889
Revolving Loans Amortized Cost Basis	22,510
Revolving Loans Converted to Term Loans Amortized Cost Basis	229
Total	74,481	68,032
Accrued interest	133
Commercial Loans | Commercial and industrial
Financing Receivable, Credit Quality Indicator [Line Items]
2020	13,373
2019	6,081
2018	4,739
2017	3,373
2016	2,380
Prior	3,310
Revolving Loans Amortized Cost Basis	21,593
Revolving Loans Converted to Term Loans Amortized Cost Basis	176
Total	55,025	48,295
Commercial Loans | Commercial and industrial | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
2020	13,328
2019	5,936
2018	4,512
2017	3,141
2016	2,223
Prior	3,018
Revolving Loans Amortized Cost Basis	19,876
Revolving Loans Converted to Term Loans Amortized Cost Basis	153
Total	52,187
Commercial Loans | Commercial and industrial | Criticized (Accruing)
Financing Receivable, Credit Quality Indicator [Line Items]
2020	39
2019	131
2018	164
2017	201
2016	137
Prior	251
Revolving Loans Amortized Cost Basis	1,434
Revolving Loans Converted to Term Loans Amortized Cost Basis	22
Total	2,379
Commercial Loans | Commercial and industrial | Criticized (Nonaccruing)
Financing Receivable, Credit Quality Indicator [Line Items]
2020	6
2019	14
2018	63
2017	31
2016	20
Prior	41
Revolving Loans Amortized Cost Basis	283
Revolving Loans Converted to Term Loans Amortized Cost Basis	1
Total	459
Commercial Loans | Commercial mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
2020	1,344
2019	3,227
2018	1,946
2017	1,034
2016	965
Prior	3,603
Revolving Loans Amortized Cost Basis	892
Revolving Loans Converted to Term Loans Amortized Cost Basis	48
Total	13,059	13,491
Commercial Loans | Commercial mortgage | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
2020	1,341
2019	3,186
2018	1,877
2017	918
2016	879
Prior	3,267
Revolving Loans Amortized Cost Basis	807
Revolving Loans Converted to Term Loans Amortized Cost Basis	46
Total	12,321
Commercial Loans | Commercial mortgage | Criticized (Accruing)
Financing Receivable, Credit Quality Indicator [Line Items]
2020	3
2019	40
2018	65
2017	113
2016	85
Prior	246
Revolving Loans Amortized Cost Basis	80
Revolving Loans Converted to Term Loans Amortized Cost Basis	2
Total	634
Commercial Loans | Commercial mortgage | Criticized (Nonaccruing)
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	1
2018	4
2017	3
2016	1
Prior	90
Revolving Loans Amortized Cost Basis	5
Revolving Loans Converted to Term Loans Amortized Cost Basis	0
Total	104
Commercial Loans | Real estate — construction
Financing Receivable, Credit Quality Indicator [Line Items]
2020	242
2019	704
2018	642
2017	226
2016	75
Prior	28
Revolving Loans Amortized Cost Basis	25
Revolving Loans Converted to Term Loans Amortized Cost Basis	5
Total	1,947	1,558
Commercial Loans | Real estate — construction | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
2020	242
2019	701
2018	624
2017	226
2016	34
Prior	25
Revolving Loans Amortized Cost Basis	24
Revolving Loans Converted to Term Loans Amortized Cost Basis	5
Total	1,881
Commercial Loans | Real estate — construction | Criticized (Accruing)
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	3
2018	18
2017	0
2016	41
Prior	2
Revolving Loans Amortized Cost Basis	1
Revolving Loans Converted to Term Loans Amortized Cost Basis	0
Total	65
Commercial Loans | Real estate — construction | Criticized (Nonaccruing)
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	0
2017	0
Prior	1
Revolving Loans Amortized Cost Basis	0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0
Total	1
Commercial Loans | Commercial lease financing
Financing Receivable, Credit Quality Indicator [Line Items]
2020	802
2019	1,194
2018	639
2017	582
2016	285
Prior	948
Revolving Loans Converted to Term Loans Amortized Cost Basis	0
Total	4,450	$ 4,688
Commercial Loans | Commercial lease financing | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
2020	793
2019	1,180
2018	620
2017	561
2016	273
Prior	939
Revolving Loans Amortized Cost Basis	0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0
Total	4,366
Commercial Loans | Commercial lease financing | Criticized (Accruing)
Financing Receivable, Credit Quality Indicator [Line Items]
2020	9
2019	14
2018	18
2017	19
2016	9
Prior	9
Revolving Loans Amortized Cost Basis	0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0
Total	78
Commercial Loans | Commercial lease financing | Criticized (Nonaccruing)
Financing Receivable, Credit Quality Indicator [Line Items]
2020	0
2019	0
2018	1
2017	2
2016	3
Prior	0
Revolving Loans Amortized Cost Basis	0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0
Total	$ 6