Other Assets (Schedule of Other Assets) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Other Assets [Abstract]
Property and equipment at cost	$ 1,203	$ 1,064
Accumulated depreciation, property and equipment	(667)	(608)
Property and equipment, net	536	456
Nonmarketable equity securities	1,235	1,233
Restricted cash collections for securitization trusts	695	812
Accrued interest and rent receivables	588	550
Net deferred tax assets	432	461
Goodwill	240	240
Restricted cash and cash equivalents	132	94
Other accounts receivable	119	116
Cash reserve deposits held for securitization trusts	108	111
Derivative contracts in a receivable position, fair value	70	39
Cash collateral placed with counterparties	68	29
Other assets	1,573	1,522
Total other assets	5,796	5,663
Federal Home Loan Bank stock	732	745
Federal Reserve Bank stock	447	445
Equity securities without a readily determinable fair value	56
Impairment related to equity securities without a readily determinable fair value	1
Goodwill [Line Items]
Goodwill	240	240
Insurance operations
Other Assets [Abstract]
Goodwill	27	27
Goodwill [Line Items]
Goodwill	27	27
Corporate and Other
Other Assets [Abstract]
Goodwill	193	193
Goodwill [Line Items]
Goodwill	193	193
Automotive Finance operations
Other Assets [Abstract]
Goodwill	20	20
Goodwill [Line Items]
Goodwill	$ 20	$ 20