Discontinued Operations - Financial Information for Discontinued Operations (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income from discontinued operations, net of tax	$ 0	$ 23
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		131
Interest expense		23
Other expenses		77
Total costs and expenses		100
Income from discontinued operations before income taxes		31
Loss on sale of discontinued operations before income taxes		0
Income from discontinued operations before income taxes		31
Income tax provision		8
Income from discontinued operations, net of tax		$ 23