Related Party Transactions (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Apr. 30, 2016	Dec. 31, 2015
Related Party Transaction [Line Items]
Advances drawn on lines of credit due from GM	$ 850		$ 850			$ 573
Junior Subordinated Revolving Credit Facility [Member]
Related Party Transaction [Line Items]
Junior Subordinated Revolving Credit Facility					$ 1,000
Affiliated Entity [Member]
Related Party Transaction [Line Items]
Advances drawn on lines of credit due from GM	466		466			190
Subvention receivable	384		384			383
Interest subvention earned	119	$ 89	331	$ 252
Leased vehicle subvention earned	593	294	1,592	626
Affiliated Entity [Member] | Junior Subordinated Revolving Credit Facility [Member]
Related Party Transaction [Line Items]
Junior Subordinated Revolving Credit Facility	415		415			0
Affiliated Entity [Member] | Commercial Finance Receivables [Member]
Related Party Transaction [Line Items]
Commercial finance receivables, net due from dealers consolidated by GM	338		338			229
Commercial loan funding payable	399		399			$ 351
Parent Company [Member]
Related Party Transaction [Line Items]
Revenue from related parties	$ 1,000	$ 1,200	$ 3,200	$ 2,500