Revenue from Contracts with Customers (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 968	$ 908	$ 852
All other revenue	1,045	670	1,187
Total other revenue	2,013	1,578	2,039
Remarketing gains (losses), net	211	170	344
Corporate and Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	133	112	80
All other revenue	11	(12)	141
Total other revenue	144	100	221
Automotive Finance operations
Disaggregation of Revenue [Line Items]
Remarketing gains (losses), net	211	170	344
Automotive Finance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	135	127	129
All other revenue	186	179	122
Total other revenue	321	306	251
Insurance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	700	669	643
All other revenue	728	354	702
Total other revenue	1,428	1,023	1,345
Mortgage Finance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
All other revenue	16	27	94
Total other revenue	16	27	94
Corporate Finance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
All other revenue	104	122	128
Total other revenue	104	122	128
Noninsurance contracts
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	686	655	627
Noninsurance contracts | Corporate and Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Noninsurance contracts | Automotive Finance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Noninsurance contracts | Insurance operations
Disaggregation of Revenue [Line Items]
Unearned revenue, remaining performance obligation, amount	3,000	3,000	3,100	$ 3,000
Unearned revenue, revenue recognized	973	939	909
Capitalized contract cost, net	1,800	1,800	1,900
Capitalized contract cost, amortization	580	564	537
Noninsurance contracts | Insurance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	686	655	627
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	$ 880
Remaining performance obligation, expected timing of satisfaction, period	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	$ 717
Remaining performance obligation, expected timing of satisfaction, period	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	$ 554
Remaining performance obligation, expected timing of satisfaction, period	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	$ 382
Remaining performance obligation, expected timing of satisfaction, period	1 year
Noninsurance contracts | Insurance operations | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2028-01-01
Disaggregation of Revenue [Line Items]
Unearned revenue, remaining performance obligation, amount	$ 427
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
Noninsurance contracts | Corporate Finance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Remarketing fee income
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	117	107	107
Remarketing fee income | Corporate and Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Remarketing fee income | Automotive Finance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	117	107	107
Remarketing fee income | Insurance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Remarketing fee income | Mortgage Finance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Remarketing fee income | Corporate Finance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Brokerage commissions and other revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	89	64	58
Brokerage commissions and other revenue | Corporate and Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	89	64	58
Brokerage commissions and other revenue | Automotive Finance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	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
Brokerage commissions and other revenue | Mortgage Finance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	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
Banking fees and interchange income
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	44	44	18
Customer rewards expense	20	14	1
Banking fees and interchange income | Corporate and Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	44	44	18
Banking fees and interchange income | Automotive Finance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	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
Banking fees and interchange income | Mortgage Finance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	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
Brokered/agent commissions
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	13	14	16
Brokered/agent commissions | Corporate and Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Brokered/agent commissions | Automotive Finance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Brokered/agent commissions | Insurance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	13	14	16
Brokered/agent commissions | Mortgage Finance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Brokered/agent commissions | Corporate Finance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	19	24	26
Other | Corporate and Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	4	4
Other | Automotive Finance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	18	20	22
Other | Insurance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1	0	0
Other | Mortgage Finance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0
Other | Corporate Finance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 0	$ 0	$ 0