Revenue from Contracts with Customers (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024	Mar. 31, 2025	Dec. 31, 2024	Mar. 31, 2024	Dec. 31, 2023
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 312	$ 324	$ 635	$ 568
All other revenue	254	181	(6)	467
Total other revenue	566	505	629	1,035
Remarketing gains (loss), net	0	59	(19)	105
Corporate and Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	27	36	67	68
All other revenue	1	8	(466)	2
Total other revenue	28	44	(399)	70
Automotive Finance operations
Disaggregation of Revenue [Line Items]
Remarketing gains (loss), net		59	(19)	105
Automotive Finance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	36	34	72	69
All other revenue	61	59	122	121
Total other revenue	97	93	194	190
Insurance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	249	254	496	431
All other revenue	173	84	290	291
Total other revenue	422	338	786	722
Corporate Finance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
All other revenue	19	30	48	53
Total other revenue	19	30	48	53
Noninsurance contracts
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	241	247	482	420
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	$ 2,900	$ 3,000
Unearned revenue, revenue recognized	238	244	476	488
Capitalized contract cost, net	1,800	1,800	1,800	1,800	$ 1,800	$ 1,800	$ 1,800	$ 1,800
Capitalized contract cost, amortization	135	144	276	291
Noninsurance contracts | Insurance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	241	247	482	420
Noninsurance contracts | Insurance operations | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2025-07-01
Disaggregation of Revenue [Line Items]
Unearned revenue, remaining performance obligation, amount	$ 445		$ 445
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]: 2026-01-01
Disaggregation of Revenue [Line Items]
Unearned revenue, remaining performance obligation, amount	$ 781		$ 781
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	$ 639		$ 639
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	$ 482		$ 482
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]: 2029-01-01
Disaggregation of Revenue [Line Items]
Unearned revenue, remaining performance obligation, amount	$ 639		$ 639
Remaining performance obligation, expected timing of satisfaction, period
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	31	30	62	60
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	31	30	62	60
Remarketing fee income | Insurance 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	20	22	40	45
Brokerage commissions and other revenue | Corporate and Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	20	22	40	45
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 | 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	6	14	25	23
Customer rewards expense		7	6	13
Banking fees and interchange income | Corporate and Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	6	14	25	23
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 | 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	7	6	12	10
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	7	6	12	10
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	7	5	14	10
Other | Corporate and Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1	0	2	0
Other | Automotive Finance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	5	4	10	9
Other | Insurance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1	1	2	1
Other | Corporate Finance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 0	$ 0	$ 0	$ 0