Other Assets (Schedule of Other Assets) (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2018	Dec. 31, 2017
Other Assets [Abstract]
Property, Plant and Equipment, Gross	$ 1,161	$ 1,161	$ 1,064
Accumulated Depreciation, Depletion and Amortization, Property Plant and Equipment	(648)	(648)	(608)
Property, Plant and Equipment, Net	513	513	456
Nonmarketable equity securities	1,276	1,276	1,233
Restricted cash collections for securitization trusts	796	796	812
Interest Receivable	548	548	550
Deferred Tax Assets, Net	455	455	461
Accounts and Other Receivables, Net, Current	289	289	116
Goodwill	240	240	240
Restricted Cash and Cash Equivalents	116	116	94
Cash reserve deposits held for securitization trusts	103	103	111
Derivative Asset, Fair Value, Gross Asset	63	63	39
Cash and securities collateral placed with counterparties	35	35	29
Other Assets, Miscellaneous	1,580	1,580	1,522
Other Assets	6,014	6,014	5,663
Federal Home Loan Bank Stock	790	790	745
Federal Reserve Bank Stock	447	447	445
Equity Securities without a Readily Determinable Fair Value	39	39
Goodwill [Line Items]
Goodwill	240	240	240
Equity Securities without a Readily Determinable Fair Value, Impairment	1	1
Insurance Operations [Member]
Other Assets [Abstract]
Goodwill	27	27	27
Goodwill [Line Items]
Goodwill	27	27	27
Corporate and Other [Member]
Other Assets [Abstract]
Goodwill	193	193	193
Goodwill [Line Items]
Goodwill	193	193	193
Automotive Finance Operations [Member]
Other Assets [Abstract]
Goodwill	20	20	20
Goodwill [Line Items]
Goodwill	$ 20	$ 20	$ 20