Finance Receivables and Loans, Net (Troubled Debt Restructurings) (Details) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Financing Receivable, Troubled Debt Restructuring
Financing receivable, modifications, gross carrying value	$ 1,700		$ 1,700		$ 867
Loans and leases receivable, impaired, commitment to lend	$ 18		$ 18		$ 17
Financing receivable, modifications, number of loans	30,812	7,208	74,993	20,281
Financing receivable, modifications, pre-modification gross carrying value	$ 606	$ 155	$ 1,352	$ 449
Financing receivable, modifications, post-modification gross carrying value	$ 587	$ 138	$ 1,264	$ 387
Consumer portfolio segment
Financing Receivable, Troubled Debt Restructuring
Financing receivable, modifications, number of loans	30,808	7,206	74,985	20,272
Financing receivable, modifications, pre-modification gross carrying value	$ 541	$ 125	$ 1,226	$ 356
Financing receivable, modifications, post-modification gross carrying value	$ 526	$ 108	$ 1,163	$ 310
Consumer portfolio segment \| Automotive loan
Financing Receivable, Troubled Debt Restructuring
Financing receivable, modifications, number of loans	30,794	7,197	74,887	20,222
Financing receivable, modifications, pre-modification gross carrying value	$ 540	$ 124	$ 1,203	$ 349
Financing receivable, modifications, post-modification gross carrying value	$ 525	$ 107	$ 1,140	$ 303
Loans modified as a result of macroeconomic and other factors			26,132
Pre and post modification amount of loans modified as a result of macroeconomic and other factors			$ 369
Consumer portfolio segment \| Real estate-backed loan
Financing Receivable, Troubled Debt Restructuring
Financing receivable, modifications, number of loans	14	9	98	50
Financing receivable, modifications, pre-modification gross carrying value	$ 1	$ 1	$ 23	$ 7
Financing receivable, modifications, post-modification gross carrying value	$ 1	$ 1	$ 23	$ 7
Consumer portfolio segment \| Mortgage Finance operations
Financing Receivable, Troubled Debt Restructuring
Financing receivable, modifications, number of loans	2	1	31	4
Financing receivable, modifications, pre-modification gross carrying value	$ 0	$ 0	$ 15	$ 0
Financing receivable, modifications, post-modification gross carrying value	$ 0	$ 0	$ 15	$ 0
Loans modified as a result of macroeconomic and other factors			27
Pre and post modification amount of loans modified as a result of macroeconomic and other factors			$ 14
Consumer portfolio segment \| Mortgage - Legacy
Financing Receivable, Troubled Debt Restructuring
Financing receivable, modifications, number of loans	12	8	67	46
Financing receivable, modifications, pre-modification gross carrying value	$ 1	$ 1	$ 8	$ 7
Financing receivable, modifications, post-modification gross carrying value	$ 1	$ 1	$ 8	$ 7
Loans modified as a result of macroeconomic and other factors	3		38
Pre and post modification amount of loans modified as a result of macroeconomic and other factors	$ 1		$ 5
Commercial portfolio segment
Financing Receivable, Troubled Debt Restructuring
Financing receivable, modifications, number of loans	4	2	8	9
Financing receivable, modifications, pre-modification gross carrying value	$ 65	$ 30	$ 126	$ 93
Financing receivable, modifications, post-modification gross carrying value	$ 61	$ 30	$ 101	$ 77
Commercial portfolio segment \| Automotive loan
Financing Receivable, Troubled Debt Restructuring
Financing receivable, modifications, number of loans	2	1	5	7
Financing receivable, modifications, pre-modification gross carrying value	$ 7	$ 5	$ 45	$ 46
Financing receivable, modifications, post-modification gross carrying value	$ 7	$ 5	$ 40	$ 46
Commercial portfolio segment \| Other loan
Financing Receivable, Troubled Debt Restructuring
Financing receivable, modifications, number of loans	2	1	3	2
Financing receivable, modifications, pre-modification gross carrying value	$ 58	$ 25	$ 81	$ 47
Financing receivable, modifications, post-modification gross carrying value	$ 54	$ 25	$ 61	$ 31

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