Loans - TDR Disclosure - Modification to Borrowers (Details) $ in Millions	Sep. 30, 2023 USD ($)
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	$ 2,053
Current
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	1,520
30-59 days
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	156
60-89 days
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	94
Greater than 90 days
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	283
Total Delinquent Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	533
Credit Card:
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	523
Credit Card: | Current
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	318
Credit Card: | 30-59 days
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	73
Credit Card: | 60-89 days
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	48
Credit Card: | Greater than 90 days
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	84
Credit Card: | Total Delinquent Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	205
Credit Card: | Domestic Card
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	447
Credit Card: | Domestic Card | Current
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	283
Credit Card: | Domestic Card | 30-59 days
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	65
Credit Card: | Domestic Card | 60-89 days
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	40
Credit Card: | Domestic Card | Greater than 90 days
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	59
Credit Card: | Domestic Card | Total Delinquent Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	164
Credit Card: | International card businesses
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	76
Credit Card: | International card businesses | Current
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	35
Credit Card: | International card businesses | 30-59 days
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	8
Credit Card: | International card businesses | 60-89 days
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	8
Credit Card: | International card businesses | Greater than 90 days
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	25
Credit Card: | International card businesses | Total Delinquent Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	41
Consumer Banking:
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	610
Consumer Banking: | Current
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	467
Consumer Banking: | 30-59 days
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	79
Consumer Banking: | 60-89 days
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	46
Consumer Banking: | Greater than 90 days
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	18
Consumer Banking: | Total Delinquent Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	143
Consumer Banking: | Auto
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	600
Consumer Banking: | Auto | Current
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	457
Consumer Banking: | Auto | 30-59 days
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	79
Consumer Banking: | Auto | 60-89 days
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	46
Consumer Banking: | Auto | Greater than 90 days
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	18
Consumer Banking: | Auto | Total Delinquent Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	143
Consumer Banking: | Retail banking
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	10
Consumer Banking: | Retail banking | Current
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	10
Consumer Banking: | Retail banking | 30-59 days
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	0
Consumer Banking: | Retail banking | 60-89 days
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	0
Consumer Banking: | Retail banking | Greater than 90 days
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	0
Consumer Banking: | Retail banking | Total Delinquent Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	0
Commercial Portfolio
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	920
Commercial Portfolio | Current
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	735
Commercial Portfolio | 30-59 days
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	4
Commercial Portfolio | 60-89 days
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	0
Commercial Portfolio | Greater than 90 days
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	181
Commercial Portfolio | Total Delinquent Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	185
Commercial Portfolio | Commercial and multifamily real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	381
Commercial Portfolio | Commercial and multifamily real estate | Current
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	318
Commercial Portfolio | Commercial and multifamily real estate | 30-59 days
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	0
Commercial Portfolio | Commercial and multifamily real estate | 60-89 days
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	0
Commercial Portfolio | Commercial and multifamily real estate | Greater than 90 days
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	63
Commercial Portfolio | Commercial and multifamily real estate | Total Delinquent Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	63
Commercial Portfolio | Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	539
Commercial Portfolio | Commercial and industrial | Current
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	417
Commercial Portfolio | Commercial and industrial | 30-59 days
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	4
Commercial Portfolio | Commercial and industrial | 60-89 days
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	0
Commercial Portfolio | Commercial and industrial | Greater than 90 days
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	118
Commercial Portfolio | Commercial and industrial | Total Delinquent Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	$ 122