Discontinued Operations - Narrative (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended		10 Months Ended
	Mar. 05, 2017	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2017
Disposal Group, Disposed of by Sale, Not Discontinued Operations [Member] | Fincos [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Percent of book value received	80.00%
Consideration received	$ 1,000
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]
Loss on sale of discontinued operations before income taxes		$ 336	$ 0	$ 336	$ 0
Discontinued Operations, Held-for-sale [Member] | General Motors Holdings LLC [Member] | Forecast [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Loss on sale of discontinued operations before income taxes						$ 700