Loans - FDM Disclosure - Modification to Borrowers (Details) - USD ($) $ in Millions	Jun. 30, 2024	Jun. 30, 2023
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	$ 3,116	$ 1,534
Commitments to lend on loans modified in TDRs	193	48
Current
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	2,556	1,138
30-59 days
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	203	97
60-89 days
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	124	72
Greater than 90 days
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	233	227
Total Delinquent Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	560	396
Credit Card:
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	763	346
Credit Card: | Current
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	499	184
Credit Card: | 30-59 days
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	72	48
Credit Card: | 60-89 days
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	56	33
Credit Card: | Greater than 90 days
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	136	81
Credit Card: | Total Delinquent Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	264	162
Credit Card: | Domestic Card
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	646	285
Credit Card: | Domestic Card | Current
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	438	160
Credit Card: | Domestic Card | 30-59 days
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	61	42
Credit Card: | Domestic Card | 60-89 days
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	45	27
Credit Card: | Domestic Card | Greater than 90 days
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	102	56
Credit Card: | Domestic Card | Total Delinquent Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	208	125
Credit Card: | International card businesses
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	117	61
Credit Card: | International card businesses | Current
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	61	24
Credit Card: | International card businesses | 30-59 days
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	11	6
Credit Card: | International card businesses | 60-89 days
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	11	6
Credit Card: | International card businesses | Greater than 90 days
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	34	25
Credit Card: | International card businesses | Total Delinquent Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	56	37
Consumer Banking:
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	770	424
Consumer Banking: | Current
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	572	340
Consumer Banking: | 30-59 days
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	105	49
Consumer Banking: | 60-89 days
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	68	26
Consumer Banking: | Greater than 90 days
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	25	9
Consumer Banking: | Total Delinquent Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	198	84
Consumer Banking: | Auto
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	761	421
Consumer Banking: | Auto | Current
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	564	337
Consumer Banking: | Auto | 30-59 days
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	105	49
Consumer Banking: | Auto | 60-89 days
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	68	26
Consumer Banking: | Auto | Greater than 90 days
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	24	9
Consumer Banking: | Auto | Total Delinquent Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	197	84
Consumer Banking: | Retail banking
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	9	3
Consumer Banking: | Retail banking | Current
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	8	3
Consumer Banking: | Retail banking | 30-59 days
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	0	0
Consumer Banking: | Retail banking | 60-89 days
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	0	0
Consumer Banking: | Retail banking | Greater than 90 days
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	1	0
Consumer Banking: | Retail banking | Total Delinquent Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	1	0
Commercial Banking:
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	1,583	764
Commercial Banking: | Current
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	1,485	614
Commercial Banking: | 30-59 days
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	26	0
Commercial Banking: | 60-89 days
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	0	13
Commercial Banking: | Greater than 90 days
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	72	137
Commercial Banking: | Total Delinquent Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	98	150
Commercial Banking: | Commercial and multifamily real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	641	364
Commercial Banking: | Commercial and multifamily real estate | Current
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	622	339
Commercial Banking: | Commercial and multifamily real estate | 30-59 days
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	19	0
Commercial Banking: | Commercial and multifamily real estate | 60-89 days
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	0	0
Commercial Banking: | Commercial and multifamily real estate | Greater than 90 days
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	0	25
Commercial Banking: | Commercial and multifamily real estate | Total Delinquent Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	19	25
Commercial Banking: | Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	942	400
Commercial Banking: | Commercial and industrial | Current
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	863	275
Commercial Banking: | Commercial and industrial | 30-59 days
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	7	0
Commercial Banking: | Commercial and industrial | 60-89 days
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	0	13
Commercial Banking: | Commercial and industrial | Greater than 90 days
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	72	112
Commercial Banking: | Commercial and industrial | Total Delinquent Loans
Financing Receivable, Troubled Debt Restructuring [Line Items]
Total Loans	$ 79	$ 125