Revenue from Contracts with Customers (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2023	Dec. 31, 2022
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 324	$ 245	$ 568	$ 488
All other revenue	181	261	467	516
Total other revenue	505	506	1,035	1,004
Remarketing gains (losses), net	59	70	105	117
Corporate and Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	36	34	68	67
All other revenue	3	19	(9)	(7)
Total other revenue	39	53	59	60
Automotive Finance operations
Disaggregation of Revenue [Line Items]
Remarketing gains (losses), net	59	70	105	117
Automotive Finance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	34	36	69	74
All other revenue	59	47	121	86
Total other revenue	93	83	190	160
Insurance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	254	175	431	347
All other revenue	84	162	291	371
Total other revenue	338	337	722	718
Mortgage Finance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
All other revenue	5	5	11	9
Total other revenue	5	5	11	9
Corporate Finance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
All other revenue	30	28	53	57
Total other revenue	30	28	53	57
Noninsurance contracts
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	247	171	420	340
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	$ 2,900	$ 3,000	$ 3,000	$ 3,000
Unearned revenue, revenue recognized	244	243	488	484
Capitalized contract cost, net	1,800	1,800	1,800	1,800	$ 1,800	$ 1,800	$ 1,800	$ 1,800
Capitalized contract cost, amortization	144	144	291	288
Noninsurance contracts | Insurance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	247	171	420	340
Noninsurance contracts | Insurance operations | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-07-01
Disaggregation of Revenue [Line Items]
Unearned revenue, remaining performance obligation, amount	$ 454		$ 454
Remaining performance obligation, expected timing of satisfaction, period	6 months		6 months
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	$ 785		$ 785
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	$ 635		$ 635
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	$ 468		$ 468
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]: 2028-01-01
Disaggregation of Revenue [Line Items]
Unearned revenue, remaining performance obligation, amount	$ 611		$ 611
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	30	31	60	64
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	30	31	60	64
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	22	23	45	46
Brokerage commissions and other revenue | Corporate and Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	22	23	45	46
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	14	11	23	21
Customer rewards expense	7	5	13	9
Banking fees and interchange income | Corporate and Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	14	11	23	21
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	6	4	10	7
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	6	4	10	7
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	5	5	10	10
Other | Corporate and Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Other | Automotive Finance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	4	5	9	10
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