Holdings of New GM Securities - Holdings of Securities for Trust Beneficiaries (Detail) - Liquidation Basis of Accounting [Member] - USD ($) $ in Thousands	Jun. 30, 2015	Mar. 31, 2015
Distribution Made to Limited Partner [Line Items]
Fair Value	$ 790,767	$ 917,977
New GM Common Stock [Member]
Distribution Made to Limited Partner [Line Items]
Number	11,388,041
Fair Value	$ 379,563
New GM Series A Warrants [Member]
Distribution Made to Limited Partner [Line Items]
Number	10,352,556
Fair Value	$ 246,081
New GM Series B Warrants [Member]
Distribution Made to Limited Partner [Line Items]
Number	10,352,556
Fair Value	$ 165,123