Revenue from Contracts with Customers (Disaggregation of Revenue) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2019	Jan. 01, 2018
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									$ 727	$ 689
Other revenue	$ 487	$ 413	$ 395	$ 466	$ 298	$ 398	$ 364	$ 354	1,761	1,414	$ 1,544
Corporate and Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									77	75
Other revenue									171	119	81
Noninsurance contracts
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									542	506
Unearned revenue, remaining performance obligation, amount	2,900				2,600				2,900	2,600		$ 2,600	$ 2,500
Unearned revenue, revenue recognized									816	786
Capitalized contract cost, net	1,700				$ 1,500				1,700	1,500		$ 1,500	$ 1,400
Capitalized contract cost, amortization									463	427
Noninsurance contracts | Corporate and Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									0	0
Remarketing fee income
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									74	79
Remarketing fee income | Corporate and Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									0	0
Brokerage commissions and other revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									61	62
Brokerage commissions and other revenue | Corporate and Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									61	62
Deposit account and other banking fees
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									16	13
Deposit account and other banking fees | Corporate and Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									16	13
Brokered/agent commissions
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									14	15
Brokered/agent commissions | Corporate and Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									0	0
Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									20	14
Other | Corporate and Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									0	0
Out of scope of Topic 606
Disaggregation of Revenue [Line Items]
Other revenue									1,034	725
Out of scope of Topic 606 | Corporate and Other
Disaggregation of Revenue [Line Items]
Other revenue									94	44
Automotive Finance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									93	92
Other revenue									249	269	355
Automotive Finance operations | Noninsurance contracts | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									0	0
Automotive Finance operations | Remarketing fee income | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									74	79
Automotive Finance operations | Brokerage commissions and other revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									0	0
Automotive Finance operations | Deposit account and other banking fees | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									0	0
Automotive Finance operations | Brokered/agent commissions | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									0	0
Automotive Finance operations | Other | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									19	13
Automotive Finance operations | Out of scope of Topic 606 | Operating Segments
Disaggregation of Revenue [Line Items]
Other revenue									156	177
Automotive Finance operations | Sale of off-lease vehicles
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									69	90
Insurance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									557	522
Other revenue									1,274	981	1,059
Insurance operations | Noninsurance contracts | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									542	506
Insurance operations | Remarketing fee income | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									0	0
Insurance operations | Brokerage commissions and other revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									0	0
Insurance operations | Deposit account and other banking fees | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									0	0
Insurance operations | Brokered/agent commissions | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									14	15
Insurance operations | Other | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									1	1
Insurance operations | Out of scope of Topic 606 | Operating Segments
Disaggregation of Revenue [Line Items]
Other revenue									717	459
Mortgage Finance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									0	0
Other revenue									22	7	4
Mortgage Finance operations | Noninsurance contracts | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									0	0
Mortgage Finance operations | Remarketing fee income | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									0	0
Mortgage Finance operations | Brokerage commissions and other revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									0	0
Mortgage Finance operations | Deposit account and other banking fees | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									0	0
Mortgage Finance operations | Brokered/agent commissions | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									0	0
Mortgage Finance operations | Other | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									0	0
Mortgage Finance operations | Out of scope of Topic 606 | Operating Segments
Disaggregation of Revenue [Line Items]
Other revenue									22	7
Corporate Finance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									0	0
Other revenue									45	38	$ 45
Corporate Finance operations | Noninsurance contracts | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									0	0
Corporate Finance operations | Remarketing fee income | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									0	0
Corporate Finance operations | Brokerage commissions and other revenue | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									0	0
Corporate Finance operations | Deposit account and other banking fees | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									0	0
Corporate Finance operations | Brokered/agent commissions | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									0	0
Corporate Finance operations | Other | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									0	0
Corporate Finance operations | Out of scope of Topic 606 | Operating Segments
Disaggregation of Revenue [Line Items]
Other revenue									45	$ 38
2020 | Noninsurance contracts
Disaggregation of Revenue [Line Items]
Unearned revenue, remaining performance obligation, amount	768								768
2021 | Noninsurance contracts
Disaggregation of Revenue [Line Items]
Unearned revenue, remaining performance obligation, amount	682								682
2022 | Noninsurance contracts
Disaggregation of Revenue [Line Items]
Unearned revenue, remaining performance obligation, amount	569								569
2023 | Noninsurance contracts
Disaggregation of Revenue [Line Items]
Unearned revenue, remaining performance obligation, amount	433								433
2024 and thereafter | Noninsurance contracts
Disaggregation of Revenue [Line Items]
Unearned revenue, remaining performance obligation, amount	$ 417								$ 417