Revenue from Contracts with Customers (Disaggregation of Revenue) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 179	$ 183	$ 365	$ 362
Other revenue	555	395	821	861
Remarketing losses (gains), net	11	(23)	9	(38)
Corporate and Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	15	21	32	43
Other revenue	52	34	111	59
Automotive Finance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	18	24	40	47
Other revenue	40	61	87	129
Insurance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	146	138	293	272
Other revenue	438	286	575	646
Mortgage Finance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Other revenue	19	4	29	6
Corporate Finance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Other revenue	6	10	19	21
Noninsurance contracts
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	142	134	285	265
Unearned revenue, remaining performance obligation, amount	2,900	2,800	2,900	2,800	$ 2,900	$ 2,900	$ 2,700	$ 2,600
Unearned revenue, revenue recognized	211	202	425	401
Capitalized contract cost, net	1,800	1,600	1,800	1,600	$ 1,700	$ 1,700	$ 1,600	$ 1,500
Capitalized contract cost, amortization	121	114	246	225
Noninsurance contracts | 2020
Disaggregation of Revenue [Line Items]
Unearned revenue, remaining performance obligation, amount	406		406
Noninsurance contracts | 2021
Disaggregation of Revenue [Line Items]
Unearned revenue, remaining performance obligation, amount	747		747
Noninsurance contracts | 2022
Disaggregation of Revenue [Line Items]
Unearned revenue, remaining performance obligation, amount	649		649
Noninsurance contracts | 2023
Disaggregation of Revenue [Line Items]
Unearned revenue, remaining performance obligation, amount	520		520
Noninsurance contracts | 2024 and thereafter
Disaggregation of Revenue [Line Items]
Unearned revenue, remaining performance obligation, amount	596		596
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 | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	142	134	285	265
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	15	19	32	37
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	15	19	32	37
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	14	17	27	34
Brokerage commissions and other revenue | Corporate and Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	14	17	27	34
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
Brokered/agent commissions
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	4	4	8	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	4	4	8	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
Deposits and Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1	4	5	9
Deposits and Banking | Corporate and Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1	4	5	9
Deposits and Banking | Automotive Finance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Deposits and Banking | Insurance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Deposits and Banking | Mortgage Finance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	0
Deposits and Banking | 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	3	5	8	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	3	5	8	10
Other | Insurance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	0	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
Out of scope of Topic 606
Disaggregation of Revenue [Line Items]
Other revenue	376	212	456	499
Out of scope of Topic 606 | Corporate and Other
Disaggregation of Revenue [Line Items]
Other revenue	37	13	79	16
Out of scope of Topic 606 | Automotive Finance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Other revenue	22	37	47	82
Out of scope of Topic 606 | Insurance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Other revenue	292	148	282	374
Out of scope of Topic 606 | Mortgage Finance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Other revenue	19	4	29	6
Out of scope of Topic 606 | Corporate Finance operations | Operating Segments
Disaggregation of Revenue [Line Items]
Other revenue	$ 6	$ 10	$ 19	$ 21