Loans and Card Member Receivables - Aging by Origination Year (Details) - Other Loans - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2025	Dec. 31, 2024
Accounts, Notes, Loans and Financing Receivable [Line Items]
Threshold period past due	30 days
2025/2024	$ 4,519	$ 4,964
2024/2023	2,708	1,591
2023/2022	695	362
2022/2021	67	10
2021/2020	7	14
Prior	60	58
Revolving Loans	2,462	2,233
Total	10,518	9,232
2025/2024, gross write-offs	6	13
2024/2023, gross write-offs	56	59
2023/2022, gross write-offs	39	42
2022/2021, gross write-offs	11	6
2021/2020, gross write-offs	1	0
Prior, gross write-offs	0	0
Revolving Loans, gross write-offs	65	87
Total gross write-offs	178	207
Loans over 90 days past due and accruing interest	7	6
Non-accruals	19	19
Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
2025/2024	4,513	4,950
2024/2023	2,690	1,578
2023/2022	686	356
2022/2021	65	10
2021/2020	7	14
Prior	58	57
Revolving Loans	2,440	2,209
Total	10,459	9,174
30 to 59 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
2025/2024	3	5
2024/2023	7	5
2023/2022	3	2
2022/2021	1	0
2021/2020	0	0
Prior	1	0
Revolving Loans	8	10
Total	23	22
60 to 89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
2025/2024	2	5
2024/2023	6	4
2023/2022	3	2
2022/2021	0	0
2021/2020	0	0
Prior	0	0
Revolving Loans	7	7
Total	18	18
90+ Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
2025/2024	1	4
2024/2023	5	4
2023/2022	3	2
2022/2021	1	0
2021/2020	0	0
Prior	1	1
Revolving Loans	7	7
Total	$ 18	$ 18