Discontinued Operations - Financial Information for Discontinued Operations (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income (loss) from discontinued operations, net of tax	$ 0	$ 16	$ 0	$ (169)
Discontinued Operations, Held-for-sale [Member] | General Motors Holdings LLC [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total revenue		148		422
Interest expense		24		70
Other expenses		75		231
Total costs and expenses		99		301
Income from discontinued operations before income taxes		49		121
Loss on sale of discontinued operations before income taxes		38		374
Income (loss) from discontinued operations before income taxes		11		(253)
Income tax benefit		(5)		(84)
Income (loss) from discontinued operations, net of tax		$ 16		$ (169)