Segment Information (Financial Information Operating Segments) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Segment Reporting Information [Line Items]
Net Financing Revenue	$ 1,049	$ 979
Nonoperating Income (Expense)	354	396
Revenue, Net	1,403	1,375
Provision for Loan Losses Expensed	261	271
Noninterest Expense	814	778
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	328	326
Assets	170,021	162,101	$ 167,148
Interest Income (Expense), after Provision for Loan Loss	788	708
Automotive Finance Operations [Member]
Segment Reporting Information [Line Items]
Net Financing Revenue	909	892
Nonoperating Income (Expense)	66	101
Revenue, Net	975	993
Provision for Loan Losses Expensed	259	268
Noninterest Expense	448	437
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	268	288
Assets	114,934	115,154
Insurance Operations Member
Segment Reporting Information [Line Items]
Net Financing Revenue	12	15
Nonoperating Income (Expense)	246	264
Revenue, Net	258	279
Provision for Loan Losses Expensed	0	0
Noninterest Expense	231	239
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	27	40
Assets	7,557	7,230
Mortgage Finance Operations [Member]
Segment Reporting Information [Line Items]
Net Financing Revenue	43	34
Nonoperating Income (Expense)	1	0
Revenue, Net	44	34
Provision for Loan Losses Expensed	2	1
Noninterest Expense	34	24
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	8	9
Assets	12,780	8,362
Corporate Finance Operations [Member]
Segment Reporting Information [Line Items]
Net Financing Revenue	46	34
Nonoperating Income (Expense)	8	18
Revenue, Net	54	52
Provision for Loan Losses Expensed	0	6
Noninterest Expense	25	21
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	29	25
Assets	4,375	3,438
Corporate and Other [Member]
Segment Reporting Information [Line Items]
Net Financing Revenue	39	4
Nonoperating Income (Expense)	33	13
Revenue, Net	72	17
Provision for Loan Losses Expensed	0	(4)
Noninterest Expense	76	57
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	(4)	(36)
Assets	$ 30,375	$ 27,917