Related Party Transactions - Related Party Payables (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Affiliated Entity [Member]
Related Party Transaction [Line Items]
Subvention receivable	$ 727	$ 306
Leased vehicle subvention earned	3,274	3,046	$ 2,232
Affiliated Entity [Member] \| Retail Finance Receivables [Member]
Related Party Transaction [Line Items]
Commercial finance receivables, net due from dealers consolidated by GM	134	88
Interest subvention earned	487	438	337
Affiliated Entity [Member] \| Commercial Finance Receivables [Member]
Related Party Transaction [Line Items]
Commercial finance receivables, net due from dealers consolidated by GM	445	355
Commercial loan funding payable	61	90
Interest subvention earned	67	54	50
GM [Member]
Related Party Transaction [Line Items]
Revenue from related parties	$ 3,800	$ 4,300	$ 4,200

Related Party, Leased Vehicle Income Earned

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