Other Assets (Schedule of Other Assets) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Other Assets [Abstract]
Property, Plant and Equipment, Gross	$ 1,107	$ 1,064
Accumulated Depreciation, Depletion and Amortization, Property Plant and Equipment	(627)	(608)
Property, Plant and Equipment, Net	480	456
Nonmarketable equity securities	1,250	1,233
Restricted cash collections for securitization trusts	986	812
Interest Receivable	533	550
Deferred Tax Assets, Net	530	461
Goodwill	240	240
Accounts and Other Receivables, Net, Current	142	116
Restricted Cash and Cash Equivalents	119	94
Cash reserve deposits held for securitization trusts	112	111
Derivative Asset, Fair Value, Gross Asset	56	39
Cash and securities collateral placed with counterparties	33	29
Other Assets, Miscellaneous	1,544	1,522
Other Assets	6,025	5,663
Federal Home Loan Bank Stock	764	745
Federal Reserve Bank Stock	446	445
Equity Securities, Fair Value	40
Goodwill [Line Items]
Goodwill	240	240
Insurance Operations Member
Other Assets [Abstract]
Goodwill	27	27
Goodwill [Line Items]
Goodwill	27	27
Corporate and Other [Member]
Other Assets [Abstract]
Goodwill	193	193
Goodwill [Line Items]
Goodwill	193	193
Automotive Finance Operations [Member]
Other Assets [Abstract]
Goodwill	20	20
Goodwill [Line Items]
Goodwill	$ 20	$ 20