Revenue from Contracts with Customers (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Jun. 30, 2023	Dec. 31, 2022	Jun. 30, 2022	Dec. 31, 2021
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 242	$ 228	$ 730	$ 675
All other revenue	193	69	709	376
Total other revenue	435	297	1,439	1,051
Remarketing gains (losses), net	57	39	174	139
Corporate and Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	33	30	100	77
All other revenue	2	(104)	(5)	(26)
Total other revenue	35	(74)	95	51
Automotive Finance operations
Disaggregation of Revenue [Line Items]
Remarketing gains (losses), net	57	39	174	139
Automotive Finance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	32	31	106	98
All other revenue	47	43	133	116
Total other revenue	79	74	239	214
Insurance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	177	167	524	500
All other revenue	116	69	487	164
Total other revenue	293	236	1,011	664
Mortgage Finance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
All other revenue	4	7	13	25
Total other revenue	4	7	13	25
Corporate Finance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
All other revenue	24	54	81	97
Total other revenue	24	54	81	97
Noninsurance contracts
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	173	164	513	489
Noninsurance contracts | Corporate and Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Noninsurance contracts | Automotive Finance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Noninsurance contracts | Insurance operations
Disaggregation of Revenue [Line Items]
Unearned revenue, remaining performance obligation, amount	3,000	3,000	3,000	3,000	$ 3,000	$ 3,000	$ 3,000	$ 3,100
Unearned revenue, revenue recognized	249	236	733	701
Capitalized contract cost, net	1,800	1,800	1,800	1,800	$ 1,800	$ 1,800	$ 1,800	$ 1,900
Capitalized contract cost, amortization	148	143	436	420
Noninsurance contracts | Insurance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	173	164	513	489
Noninsurance contracts | Insurance operations | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-10-01
Disaggregation of Revenue [Line Items]
Unearned revenue, remaining performance obligation, amount	$ 238		$ 238
Remaining performance obligation, expected timing of satisfaction, period	3 months		3 months
Noninsurance contracts | Insurance operations | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-01-01
Disaggregation of Revenue [Line Items]
Unearned revenue, remaining performance obligation, amount	$ 845		$ 845
Remaining performance obligation, expected timing of satisfaction, period	1 year		1 year
Noninsurance contracts | Insurance operations | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2025-01-01
Disaggregation of Revenue [Line Items]
Unearned revenue, remaining performance obligation, amount	$ 683		$ 683
Remaining performance obligation, expected timing of satisfaction, period	1 year		1 year
Noninsurance contracts | Insurance operations | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2026-01-01
Disaggregation of Revenue [Line Items]
Unearned revenue, remaining performance obligation, amount	$ 513		$ 513
Remaining performance obligation, expected timing of satisfaction, period	1 year		1 year
Noninsurance contracts | Insurance operations | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2027-01-01
Disaggregation of Revenue [Line Items]
Unearned revenue, remaining performance obligation, amount	$ 695		$ 695
Remaining performance obligation, expected timing of satisfaction, period
Noninsurance contracts | Mortgage Finance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 0	0	$ 0	0
Noninsurance contracts | Corporate Finance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Remarketing fee income
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	27	26	91	82
Remarketing fee income | Corporate and Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Remarketing fee income | Automotive Finance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	27	26	91	82
Remarketing fee income | Insurance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Remarketing fee income | Mortgage Finance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Remarketing fee income | Corporate Finance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Brokerage commissions and other revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	23	18	69	42
Brokerage commissions and other revenue | Corporate and Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	23	18	69	42
Brokerage commissions and other revenue | Automotive Finance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Brokerage commissions and other revenue | Insurance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Brokerage commissions and other revenue | Mortgage Finance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Brokerage commissions and other revenue | Corporate Finance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Banking fees and interchange income
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	10	11	31	32
Customer rewards expense	5	4	14	10
Banking fees and interchange income | Corporate and Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	10	11	31	32
Banking fees and interchange income | Automotive Finance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Banking fees and interchange income | Insurance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Banking fees and interchange income | Mortgage Finance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Banking fees and interchange income | Corporate Finance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Brokered/agent commissions
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	3	3	10	11
Brokered/agent commissions | Corporate and Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Brokered/agent commissions | Automotive Finance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Brokered/agent commissions | Insurance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	3	3	10	11
Brokered/agent commissions | Mortgage Finance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Brokered/agent commissions | Corporate Finance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	6	6	16	19
Other | Corporate and Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	1	0	3
Other | Automotive Finance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	5	5	15	16
Other | Insurance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1	0	1	0
Other | Mortgage Finance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Other | Corporate Finance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 0	$ 0	$ 0	$ 0