Related Party Transactions (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Related Party Transaction [Line Items]
Advances drawn on lines of credit due from GM	$ 1,076		$ 573
Affiliated Entity [Member]
Related Party Transaction [Line Items]
Advances drawn on lines of credit due from GM	640		190
Subvention receivable	436		383
Interest subvention earned	103	$ 78
Leased vehicle subvention earned	(459)	(136)
Affiliated Entity [Member] | Commercial Finance Receivables [Member]
Related Party Transaction [Line Items]
Financing receivable, net	288		229
Commercial loan funding payable	435		$ 351
Parent Company [Member]
Related Party Transaction [Line Items]
Revenue from related parties	$ 1,200	$ 500