Asset Quality - Commercial Credit Exposure (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Financing Receivable, Credit Quality Indicator [Line Items]
Total	$ 98,609	$ 101,185
Accrued interest	211	241
Commercial Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current	13,562	16,230
One year prior	8,364	10,657
Two years prior	8,782	7,206
Three years prior	5,554	4,635
Four years prior	3,556	3,237
Prior	8,500	7,295
Revolving Loans Amortized Cost Basis	20,807	22,529
Revolving Loans Converted to Term Loans Amortized Cost Basis	204	191
Total	69,329	71,980
Accrued interest	117	140
Commercial Loans | Commercial and Industrial
Financing Receivable, Credit Quality Indicator [Line Items]
Current	9,355	13,174
One year prior	5,544	5,712
Two years prior	4,702	4,285
Three years prior	3,419	2,881
Four years prior	2,258	2,134
Prior	4,108	2,995
Revolving Loans Amortized Cost Basis	20,035	21,585
Revolving Loans Converted to Term Loans Amortized Cost Basis	132	141
Total	49,553	52,907
Commercial Loans | Commercial and Industrial | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Current	9,315	13,100
One year prior	5,420	5,487
Two years prior	4,491	4,040
Three years prior	3,186	2,617
Four years prior	2,016	1,967
Prior	3,884	2,709
Revolving Loans Amortized Cost Basis	18,950	19,832
Revolving Loans Converted to Term Loans Amortized Cost Basis	102	118
Total	47,364	49,870
Commercial Loans | Commercial and Industrial | Criticized (Accruing)
Financing Receivable, Credit Quality Indicator [Line Items]
Current	40	66
One year prior	115	198
Two years prior	193	174
Three years prior	192	236
Four years prior	236	150
Prior	208	279
Revolving Loans Amortized Cost Basis	925	1,527
Revolving Loans Converted to Term Loans Amortized Cost Basis	27	22
Total	1,936	2,652
Commercial Loans | Commercial and Industrial | Criticized (Nonaccruing)
Financing Receivable, Credit Quality Indicator [Line Items]
Current	0	8
One year prior	9	27
Two years prior	18	71
Three years prior	41	28
Four years prior	6	17
Prior	16	7
Revolving Loans Amortized Cost Basis	160	226
Revolving Loans Converted to Term Loans Amortized Cost Basis	3	1
Total	253	385
Commercial Loans | Commercial mortgage
Financing Receivable, Credit Quality Indicator [Line Items]
Current	3,234	1,603
One year prior	1,378	3,080
Two years prior	2,677	1,822
Three years prior	1,428	1,016
Four years prior	811	839
Prior	3,338	3,370
Revolving Loans Amortized Cost Basis	742	912
Revolving Loans Converted to Term Loans Amortized Cost Basis	66	45
Total	13,674	12,687
Commercial Loans | Commercial mortgage | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Current	3,219	1,591
One year prior	1,357	2,937
Two years prior	2,589	1,737
Three years prior	1,338	867
Four years prior	687	765
Prior	3,073	3,027
Revolving Loans Amortized Cost Basis	690	885
Revolving Loans Converted to Term Loans Amortized Cost Basis	64	43
Total	13,017	11,852
Commercial Loans | Commercial mortgage | Criticized (Accruing)
Financing Receivable, Credit Quality Indicator [Line Items]
Current	15	12
One year prior	20	142
Two years prior	87	81
Three years prior	85	145
Four years prior	123	72
Prior	228	255
Revolving Loans Amortized Cost Basis	48	22
Revolving Loans Converted to Term Loans Amortized Cost Basis	2	2
Total	608	731
Commercial Loans | Commercial mortgage | Criticized (Nonaccruing)
Financing Receivable, Credit Quality Indicator [Line Items]
Current	0	0
One year prior	1	1
Two years prior	1	4
Three years prior	5	4
Four years prior	1	2
Prior	37	88
Revolving Loans Amortized Cost Basis	4	5
Revolving Loans Converted to Term Loans Amortized Cost Basis	0	0
Total	49	104
Commercial Loans | Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Current	318	367
One year prior	623	778
Two years prior	623	548
Three years prior	344	206
Four years prior	126	27
Prior	50	24
Revolving Loans Amortized Cost Basis	30	32
Revolving Loans Converted to Term Loans Amortized Cost Basis	6	5
Total	2,120	1,987
Commercial Loans | Construction | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Current	318	367
One year prior	619	764
Two years prior	610	510
Three years prior	292	188
Four years prior	104	27
Prior	49	22
Revolving Loans Amortized Cost Basis	29	31
Revolving Loans Converted to Term Loans Amortized Cost Basis	6	5
Total	2,027	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	13	38
Three years prior	52	18
Four years prior	22	0
Prior	1	2
Revolving Loans Amortized Cost Basis	1	1
Revolving Loans Converted to Term Loans Amortized Cost Basis	0	0
Total	93	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	655	1,086
One year prior	819	1,087
Two years prior	780	551
Three years prior	363	532
Four years prior	361	237
Prior	1,004	906
Revolving Loans Amortized Cost Basis		0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0	0
Total	3,982	4,399
Commercial Loans | Commercial lease financing | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Current	655	1,076
One year prior	815	1,050
Two years prior	744	534
Three years prior	348	504
Four years prior	347	228
Prior	997	901
Revolving Loans Amortized Cost Basis	0	0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0	0
Total	3,906	4,293
Commercial Loans | Commercial lease financing | Criticized (Accruing)
Financing Receivable, Credit Quality Indicator [Line Items]
Current	0	10
One year prior	4	35
Two years prior	35	15
Three years prior	14	26
Four years prior	13	7
Prior	5	4
Revolving Loans Amortized Cost Basis	0	0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0	0
Total	71	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	1	2
Three years prior	1	2
Four years prior	1	2
Prior	2	1
Revolving Loans Amortized Cost Basis	0	0
Revolving Loans Converted to Term Loans Amortized Cost Basis	0	0
Total	$ 5	$ 9