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Asset Quality - Breakdown of Nonperforming TDRs by Loans Category (Details) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2021 USD ($) SecurityLoan	Dec. 31, 2020 USD ($) SecurityLoan
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	6,007	6,133
Pre-modification Outstanding Recorded Investment	$ 501	$ 478
Post-modification Outstanding Recorded Investment	$ 376	$ 363
Prior-Year accruing
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	3,931	3,743
Pre-modification Outstanding Recorded Investment	$ 231	$ 184
Post-modification Outstanding Recorded Investment	$ 184	$ 134
Prior-Year accruing | Commercial Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	12	3
Pre-modification Outstanding Recorded Investment	$ 43	$ 5
Post-modification Outstanding Recorded Investment	$ 41	$ 0
Prior-Year accruing | Consumer Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	3,919	3,740
Pre-modification Outstanding Recorded Investment	$ 188	$ 179
Post-modification Outstanding Recorded Investment	$ 143	$ 134
Nonperforming financial instruments
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	2,076	2,390
Pre-modification Outstanding Recorded Investment	$ 270	$ 294
Post-modification Outstanding Recorded Investment	$ 192	$ 229
Nonperforming financial instruments | Commercial Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	62	73
Pre-modification Outstanding Recorded Investment	$ 190	$ 198
Post-modification Outstanding Recorded Investment	$ 121	$ 142
Nonperforming financial instruments | Consumer Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	2,014	2,317
Pre-modification Outstanding Recorded Investment	$ 80	$ 96
Post-modification Outstanding Recorded Investment	$ 71	$ 87
Commercial and Industrial | Prior-Year accruing | Commercial Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	12	3
Pre-modification Outstanding Recorded Investment	$ 43	$ 5
Post-modification Outstanding Recorded Investment	$ 41	$ 0
Commercial and Industrial | Nonperforming financial instruments | Commercial Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	57	66
Pre-modification Outstanding Recorded Investment	$ 128	$ 136
Post-modification Outstanding Recorded Investment	$ 87	$ 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	5	7
Pre-modification Outstanding Recorded Investment	$ 62	$ 62
Post-modification Outstanding Recorded Investment	$ 34	$ 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	5	7
Pre-modification Outstanding Recorded Investment	$ 62	$ 62
Post-modification Outstanding Recorded Investment	$ 34	$ 50
Real estate — residential mortgage | Prior-Year accruing | Consumer Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	513	485
Pre-modification Outstanding Recorded Investment	$ 44	$ 37
Post-modification Outstanding Recorded Investment	$ 39	$ 31
Real estate — residential mortgage | Nonperforming financial instruments | Consumer Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	206	258
Pre-modification Outstanding Recorded Investment	$ 25	$ 35
Post-modification Outstanding Recorded Investment	$ 24	$ 34
Home equity loans | Prior-Year accruing | Consumer Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	1,779	1,781
Pre-modification Outstanding Recorded Investment	$ 107	$ 106
Post-modification Outstanding Recorded Investment	$ 84	$ 83
Home equity loans | Nonperforming financial instruments | Consumer Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	564	630
Pre-modification Outstanding Recorded Investment	$ 35	$ 41
Post-modification Outstanding Recorded Investment	$ 32	$ 37
Consumer direct loans | Prior-Year accruing | Consumer Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	202	163
Pre-modification Outstanding Recorded Investment	$ 5	$ 4
Post-modification Outstanding Recorded Investment	$ 3	$ 3
Consumer direct loans | Nonperforming financial instruments | Consumer Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	203	212
Pre-modification Outstanding Recorded Investment	$ 4	$ 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	638	536
Pre-modification Outstanding Recorded Investment	$ 4	$ 3
Post-modification Outstanding Recorded Investment	$ 2	$ 1
Credit cards | Nonperforming financial instruments | Consumer Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	265	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	787	775
Pre-modification Outstanding Recorded Investment	$ 28	$ 29
Post-modification Outstanding Recorded Investment	$ 15	$ 16
Consumer indirect loans | Nonperforming financial instruments | Consumer Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	776	861
Pre-modification Outstanding Recorded Investment	$ 14	$ 15
Post-modification Outstanding Recorded Investment	$ 10	$ 11

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Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
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