Discontinued Operations - Financial Information for Discontinued Operations (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Loss from discontinued operations, net of tax	$ 0	$ (208)	$ 0	$ (185)
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		143		274
Interest expense		23		46
Other expenses		79		156
Total costs and expenses		102		202
Income from discontinued operations before income taxes		41		72
Loss on sale of discontinued operations before income taxes		336		336
Loss from discontinued operations before income taxes		(295)		(264)
Income tax benefit		(87)		(79)
Loss from discontinued operations, net of tax		$ (208)		$ (185)