Supplemental Information for the Consolidated Statements of Cash Flows - Noncash Activity (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Supplemental Cash Flow Elements [Abstract]
Subvention receivable from GM	$ 676	$ 727	$ 306
Commercial loan funding payable to GM	$ 74	$ 61	$ 90