Asset Quality - Commercial Credit Exposure (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Financing Receivable, Credit Quality Indicator [Line Items]
Total	$ 100,730	$ 101,185
Accrued interest	225	241
Commercial Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current	9,070	16,230
One year prior	11,208	10,657
Two years prior	9,235	7,206
Three years prior	6,053	4,635
Four years prior	3,862	3,237
Prior	8,980	7,295
Revolving Loans Amortized Cost Basis	21,229	22,529
Revolving Loans Converted to Term Loans Amortized Cost Basis	193	191
Total	69,830	71,980
Accrued interest	127	140
Commercial Loans | Commercial and Industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Current	6,794	13,174
One year prior	8,310	5,712
Two years prior	4,791	4,285
Three years prior	3,676	2,881
Four years prior	2,339	2,134
Prior	4,258	2,995
Revolving Loans Amortized Cost Basis	20,368	21,585
Revolving Loans Converted to Term Loans Amortized Cost Basis	136	141
Total	50,672	52,907
Commercial Loans | Commercial and Industrial | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Current	6,763	13,100
One year prior	8,185	5,487
Two years prior	4,542	4,040
Three years prior	3,382	2,617
Four years prior	2,124	1,967
Prior	3,974	2,709
Revolving Loans Amortized Cost Basis	19,061	19,832
Revolving Loans Converted to Term Loans Amortized Cost Basis	104	118
Total	48,135	49,870
Commercial Loans | Commercial and Industrial | Criticized (Accruing)
Financing Receivable, Credit Quality Indicator [Line Items]
Current	30	66
One year prior	118	198
Two years prior	232	174
Three years prior	242	236
Four years prior	208	150
Prior	236	279
Revolving Loans Amortized Cost Basis	1,086	1,527
Revolving Loans Converted to Term Loans Amortized Cost Basis	30	22
Total	2,182	2,652
Commercial Loans | Commercial and Industrial | Criticized (Nonaccruing)
Financing Receivable, Credit Quality Indicator [Line Items]
Current	1	8
One year prior	7	27
Two years prior	17	71
Three years prior	52	28
Four years prior	7	17
Prior	48	7
Revolving Loans Amortized Cost Basis	221	226
Revolving Loans Converted to Term Loans Amortized Cost Basis	2	1
Total	355	385
Commercial Loans | Commercial mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Current	1,690	1,603
One year prior	1,440	3,080
Two years prior	2,863	1,822
Three years prior	1,524	1,016
Four years prior	944	839
Prior	3,625	3,370
Revolving Loans Amortized Cost Basis	831	912
Revolving Loans Converted to Term Loans Amortized Cost Basis	48	45
Total	12,965	12,687
Commercial Loans | Commercial mortgage | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Current	1,678	1,591
One year prior	1,415	2,937
Two years prior	2,703	1,737
Three years prior	1,371	867
Four years prior	786	765
Prior	3,254	3,027
Revolving Loans Amortized Cost Basis	716	885
Revolving Loans Converted to Term Loans Amortized Cost Basis	46	43
Total	11,969	11,852
Commercial Loans | Commercial mortgage | Criticized (Accruing)
Financing Receivable, Credit Quality Indicator [Line Items]
Current	12	12
One year prior	25	142
Two years prior	156	81
Three years prior	152	145
Four years prior	142	72
Prior	330	255
Revolving Loans Amortized Cost Basis	111	22
Revolving Loans Converted to Term Loans Amortized Cost Basis	2	2
Total	930	731
Commercial Loans | Commercial mortgage | Criticized (Nonaccruing)
Financing Receivable, Credit Quality Indicator [Line Items]
Current	0	0
One year prior	0	1
Two years prior	4	4
Three years prior	1	4
Four years prior	16	2
Prior	41	88
Revolving Loans Amortized Cost Basis	4	5
Revolving Loans Converted to Term Loans Amortized Cost Basis	0	0
Total	66	104
Commercial Loans | Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Current	177	367
One year prior	559	778
Two years prior	714	548
Three years prior	419	206
Four years prior	174	27
Prior	50	24
Revolving Loans Amortized Cost Basis	30	32
Revolving Loans Converted to Term Loans Amortized Cost Basis	9	5
Total	2,132	1,987
Commercial Loans | Construction | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Current	177	367
One year prior	555	764
Two years prior	700	510
Three years prior	365	188
Four years prior	152	27
Prior	36	22
Revolving Loans Amortized Cost Basis	28	31
Revolving Loans Converted to Term Loans Amortized Cost Basis	9	5
Total	2,022	1,914
Commercial Loans | Construction | Criticized (Accruing)
Financing Receivable, Credit Quality Indicator [Line Items]
Current	0	0
One year prior	4	14
Two years prior	14	38
Three years prior	54	18
Four years prior	22	0
Prior	14	2
Revolving Loans Amortized Cost Basis	2	1
Revolving Loans Converted to Term Loans Amortized Cost Basis	0	0
Total	110	73
Commercial Loans | Construction | Criticized (Nonaccruing)
Financing Receivable, Credit Quality Indicator [Line Items]
Current	0	0
One year prior	0	0
Two years prior	0	0
Three years prior	0	0
Four years prior	0	0
Prior	0	0
Revolving Loans Amortized Cost Basis	0	0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0	0
Total	0	0
Commercial Loans | Commercial lease financing
Financing Receivable, Credit Quality Indicator [Line Items]
Current	409	1,086
One year prior	899	1,087
Two years prior	867	551
Three years prior	434	532
Four years prior	405	237
Prior	1,047	906
Revolving Loans Amortized Cost Basis		0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0	0
Total	4,061	4,399
Commercial Loans | Commercial lease financing | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Current	409	1,076
One year prior	880	1,050
Two years prior	825	534
Three years prior	416	504
Four years prior	380	228
Prior	1,037	901
Revolving Loans Amortized Cost Basis	0	0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0	0
Total	3,947	4,293
Commercial Loans | Commercial lease financing | Criticized (Accruing)
Financing Receivable, Credit Quality Indicator [Line Items]
Current	0	10
One year prior	19	35
Two years prior	40	15
Three years prior	17	26
Four years prior	23	7
Prior	8	4
Revolving Loans Amortized Cost Basis	0	0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0	0
Total	107	97
Commercial Loans | Commercial lease financing | Criticized (Nonaccruing)
Financing Receivable, Credit Quality Indicator [Line Items]
Current	0	0
One year prior	0	2
Two years prior	2	2
Three years prior	1	2
Four years prior	2	2
Prior	2	1
Revolving Loans Amortized Cost Basis	0	0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0	0
Total	$ 7	$ 9