Asset Quality - Breakdown of Nonperforming TDRs by Loans Category (Details) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2021 USD ($) SecurityLoan	Dec. 31, 2020 USD ($) SecurityLoan
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	5,730	6,133
Pre-modification Outstanding Recorded Investment	$ 460	$ 478
Post-modification Outstanding Recorded Investment	$ 334	$ 363
Prior-Year accruing
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	3,713	3,743
Pre-modification Outstanding Recorded Investment	$ 204	$ 184
Post-modification Outstanding Recorded Investment	$ 157	$ 134
Prior-Year accruing | Commercial Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	13	3
Pre-modification Outstanding Recorded Investment	$ 26	$ 5
Post-modification Outstanding Recorded Investment	$ 25	$ 0
Prior-Year accruing | Consumer Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	3,700	3,740
Pre-modification Outstanding Recorded Investment	$ 178	$ 179
Post-modification Outstanding Recorded Investment	$ 132	$ 134
Nonperforming financial instruments
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	2,017	2,390
Pre-modification Outstanding Recorded Investment	$ 256	$ 294
Post-modification Outstanding Recorded Investment	$ 177	$ 229
Nonperforming financial instruments | Commercial Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	45	73
Pre-modification Outstanding Recorded Investment	$ 178	$ 198
Post-modification Outstanding Recorded Investment	$ 110	$ 142
Nonperforming financial instruments | Consumer Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	1,972	2,317
Pre-modification Outstanding Recorded Investment	$ 78	$ 96
Post-modification Outstanding Recorded Investment	$ 67	$ 87
Commercial and Industrial | Prior-Year accruing | Commercial Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	13	3
Pre-modification Outstanding Recorded Investment	$ 26	$ 5
Post-modification Outstanding Recorded Investment	$ 25	$ 0
Commercial and Industrial | Nonperforming financial instruments | Commercial Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	41	66
Pre-modification Outstanding Recorded Investment	$ 112	$ 136
Post-modification Outstanding Recorded Investment	$ 65	$ 92
Commercial mortgage | Prior-Year accruing | Commercial Real Estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	0	0
Pre-modification Outstanding Recorded Investment	$ 0	$ 0
Post-modification Outstanding Recorded Investment	$ 0	$ 0
Commercial mortgage | Nonperforming financial instruments | Commercial Real Estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	4	7
Pre-modification Outstanding Recorded Investment	$ 66	$ 62
Post-modification Outstanding Recorded Investment	$ 45	$ 50
Commercial real estate loans | Prior-Year accruing | Commercial Real Estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	0	0
Pre-modification Outstanding Recorded Investment	$ 0	$ 0
Post-modification Outstanding Recorded Investment	$ 0	$ 0
Commercial real estate loans | Nonperforming financial instruments | Commercial Real Estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	4	7
Pre-modification Outstanding Recorded Investment	$ 66	$ 62
Post-modification Outstanding Recorded Investment	$ 45	$ 50
Real estate — residential mortgage | Prior-Year accruing | Consumer Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	480	485
Pre-modification Outstanding Recorded Investment	$ 40	$ 37
Post-modification Outstanding Recorded Investment	$ 34	$ 31
Real estate — residential mortgage | Nonperforming financial instruments | Consumer Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	214	258
Pre-modification Outstanding Recorded Investment	$ 25	$ 35
Post-modification Outstanding Recorded Investment	$ 23	$ 34
Home equity loans | Prior-Year accruing | Consumer Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	1,717	1,781
Pre-modification Outstanding Recorded Investment	$ 103	$ 106
Post-modification Outstanding Recorded Investment	$ 81	$ 83
Home equity loans | Nonperforming financial instruments | Consumer Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	532	630
Pre-modification Outstanding Recorded Investment	$ 35	$ 41
Post-modification Outstanding Recorded Investment	$ 30	$ 37
Consumer direct loans | Prior-Year accruing | Consumer Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	200	163
Pre-modification Outstanding Recorded Investment	$ 5	$ 4
Post-modification Outstanding Recorded Investment	$ 2	$ 3
Consumer direct loans | Nonperforming financial instruments | Consumer Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	200	212
Pre-modification Outstanding Recorded Investment	$ 3	$ 3
Post-modification Outstanding Recorded Investment	$ 3	$ 3
Credit cards | Prior-Year accruing | Consumer Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	598	536
Pre-modification Outstanding Recorded Investment	$ 4	$ 3
Post-modification Outstanding Recorded Investment	$ 1	$ 1
Credit cards | Nonperforming financial instruments | Consumer Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	291	356
Pre-modification Outstanding Recorded Investment	$ 2	$ 2
Post-modification Outstanding Recorded Investment	$ 2	$ 2
Consumer indirect loans | Prior-Year accruing | Consumer Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	705	775
Pre-modification Outstanding Recorded Investment	$ 26	$ 29
Post-modification Outstanding Recorded Investment	$ 14	$ 16
Consumer indirect loans | Nonperforming financial instruments | Consumer Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	735	861
Pre-modification Outstanding Recorded Investment	$ 13	$ 15
Post-modification Outstanding Recorded Investment	$ 9	$ 11