Holdings of New GM Securities - Holdings of Securities for Trust Beneficiaries (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Distribution Made to Limited Partner [Line Items]
Fair Value	$ 1,114,078	$ 1,591,110
New GM Common Stock [Member]
Distribution Made to Limited Partner [Line Items]
Number	15,297,307	28,714,897
Fair Value	526,533	798,849
New GM Series A Warrants [Member]
Distribution Made to Limited Partner [Line Items]
Number	13,906,391	26,104,257
Fair Value	345,435	484,492
New GM Series B Warrants [Member]
Distribution Made to Limited Partner [Line Items]
Number	13,906,391	26,104,257
Fair Value	$ 242,110	$ 307,769