Loans and Card Member Receivables - Performance (Details) - USD ($) $ in Millions	Jun. 30, 2025	Jun. 30, 2024
Current
Financing Receivable, Modifications [Line Items]
Account balances	$ 2,839	$ 3,091
30-89 Days Past Due
Financing Receivable, Modifications [Line Items]
Account balances	205	221
90+ Days Past Due
Financing Receivable, Modifications [Line Items]
Account balances	82	88
Card Member Loans | Current | Consumer
Financing Receivable, Modifications [Line Items]
Account balances	1,608	1,725
Card Member Loans | Current | Small Business
Financing Receivable, Modifications [Line Items]
Account balances	611	557
Card Member Loans | Current | Corporate
Financing Receivable, Modifications [Line Items]
Account balances	0	0
Card Member Loans | 30-89 Days Past Due | Consumer
Financing Receivable, Modifications [Line Items]
Account balances	102	103
Card Member Loans | 30-89 Days Past Due | Small Business
Financing Receivable, Modifications [Line Items]
Account balances	54	51
Card Member Loans | 30-89 Days Past Due | Corporate
Financing Receivable, Modifications [Line Items]
Account balances	0	0
Card Member Loans | 90+ Days Past Due | Consumer
Financing Receivable, Modifications [Line Items]
Account balances	40	44
Card Member Loans | 90+ Days Past Due | Small Business
Financing Receivable, Modifications [Line Items]
Account balances	22	20
Card Member Loans | 90+ Days Past Due | Corporate
Financing Receivable, Modifications [Line Items]
Account balances	0	0
Card Member Receivables | Current | Consumer
Financing Receivable, Modifications [Line Items]
Account balances	202	293
Card Member Receivables | Current | Small Business
Financing Receivable, Modifications [Line Items]
Account balances	328	427
Card Member Receivables | Current | Corporate
Financing Receivable, Modifications [Line Items]
Account balances	12	9
Card Member Receivables | 30-89 Days Past Due | Consumer
Financing Receivable, Modifications [Line Items]
Account balances	11	17
Card Member Receivables | 30-89 Days Past Due | Small Business
Financing Receivable, Modifications [Line Items]
Account balances	30	42
Card Member Receivables | 30-89 Days Past Due | Corporate
Financing Receivable, Modifications [Line Items]
Account balances	3	3
Card Member Receivables | 90+ Days Past Due | Consumer
Financing Receivable, Modifications [Line Items]
Account balances	5	6
Card Member Receivables | 90+ Days Past Due | Small Business
Financing Receivable, Modifications [Line Items]
Account balances	10	13
Card Member Receivables | 90+ Days Past Due | Corporate
Financing Receivable, Modifications [Line Items]
Account balances	3	3
Other Loans | Current
Financing Receivable, Modifications [Line Items]
Account balances	78	80
Other Loans | 30-89 Days Past Due
Financing Receivable, Modifications [Line Items]
Account balances	5	5
Other Loans | 90+ Days Past Due
Financing Receivable, Modifications [Line Items]
Account balances	$ 2	$ 2