Asset Quality - Breakdown of Nonperforming TDRs by Loans Category (Details) $ in Millions	6 Months Ended		12 Months Ended
	Jun. 30, 2020 USD ($) SecurityLoan	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($) SecurityLoan
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	6,154		6,212
Pre-modification Outstanding Recorded Investment	$ 382		$ 425
Post-modification Outstanding Recorded Investment	$ 310		$ 347
Prior-Year accruing
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	3,968		3,590
Pre-modification Outstanding Recorded Investment	$ 188		$ 211
Post-modification Outstanding Recorded Investment	$ 144		$ 164
Prior-Year accruing | Commercial Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	4		7
Pre-modification Outstanding Recorded Investment	$ 2		$ 30
Post-modification Outstanding Recorded Investment	$ 0		$ 25
Prior-Year accruing | Consumer Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	3,964		3,583
Pre-modification Outstanding Recorded Investment	$ 186		$ 181
Post-modification Outstanding Recorded Investment	$ 144		$ 139
Nonperforming financial instruments
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	2,186		2,622
Pre-modification Outstanding Recorded Investment	$ 194		$ 214
Post-modification Outstanding Recorded Investment	$ 166		$ 183
Nonperforming financial instruments | Commercial Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	58		57
Pre-modification Outstanding Recorded Investment	$ 122		$ 136
Post-modification Outstanding Recorded Investment	$ 101		$ 111
Nonperforming financial instruments | Consumer Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	2,128		2,565
Pre-modification Outstanding Recorded Investment	$ 72		$ 78
Post-modification Outstanding Recorded Investment	$ 65		$ 72
Commercial and industrial | Prior-Year accruing | Commercial Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	3		6
Pre-modification Outstanding Recorded Investment	$ 2		$ 30
Post-modification Outstanding Recorded Investment	$ 0		$ 25
Commercial and industrial | Nonperforming financial instruments | Commercial Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	50		51
Pre-modification Outstanding Recorded Investment	$ 57		$ 72
Post-modification Outstanding Recorded Investment	$ 43		$ 53
Commercial mortgage | Prior-Year accruing | Commercial Real Estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	1		1
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	8		6
Pre-modification Outstanding Recorded Investment	$ 65		$ 64
Post-modification Outstanding Recorded Investment	$ 58	$ 58
Commercial real estate loans | Prior-Year accruing | Commercial Real Estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	1		1
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	8		6
Pre-modification Outstanding Recorded Investment	$ 65		$ 64
Post-modification Outstanding Recorded Investment	$ 58		$ 58
Real estate — residential mortgage | Prior-Year accruing | Consumer Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	487		493
Pre-modification Outstanding Recorded Investment	$ 36		$ 37
Post-modification Outstanding Recorded Investment	$ 30		$ 31
Real estate — residential mortgage | Nonperforming financial instruments | Consumer Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	191		181
Pre-modification Outstanding Recorded Investment	$ 16		$ 13
Post-modification Outstanding Recorded Investment	$ 14		$ 11
Home equity loans | Prior-Year accruing | Consumer Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	1,872		1,751
Pre-modification Outstanding Recorded Investment	$ 111		$ 104
Post-modification Outstanding Recorded Investment	$ 91		$ 84
Home equity loans | Nonperforming financial instruments | Consumer Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	574		713
Pre-modification Outstanding Recorded Investment	$ 36		$ 42
Post-modification Outstanding Recorded Investment	$ 34		$ 41
Consumer direct loans | Prior-Year accruing | Consumer Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	183		139
Pre-modification Outstanding Recorded Investment	$ 4		$ 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	134		172
Pre-modification Outstanding Recorded Investment	$ 2		$ 2
Post-modification Outstanding Recorded Investment	$ 2		$ 2
Credit cards | Prior-Year accruing | Consumer Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	602		486
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	290		368
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	820		714
Pre-modification Outstanding Recorded Investment	$ 31		$ 33
Post-modification Outstanding Recorded Investment	$ 18		$ 20
Consumer indirect loans | Nonperforming financial instruments | Consumer Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Number of Loans | SecurityLoan	939		1,131
Pre-modification Outstanding Recorded Investment	$ 16		$ 19
Post-modification Outstanding Recorded Investment	$ 13		$ 16