Related Party Transactions (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Related Party Transaction [Line Items]
Advances drawn on lines of credit due from GM	$ 979		$ 979		$ 573
Affiliated Entity [Member]
Related Party Transaction [Line Items]
Advances drawn on lines of credit due from GM	614		614		190
Subvention receivable	365		365		383
Interest subvention earned	109	$ 85	212	$ 163
Leased vehicle subvention earned	540	196	999	332
Affiliated Entity [Member] | Commercial Finance Receivables [Member]
Related Party Transaction [Line Items]
Financing receivable, net	321		321		229
Commercial loan funding payable	436		436		$ 351
Parent Company [Member]
Related Party Transaction [Line Items]
Revenue from related parties	$ 1,000	$ 800	$ 2,200	$ 1,300