Holdings of New GM Securities - Holdings of Securities for Trust Beneficiaries (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	Jun. 30, 2014	Mar. 31, 2014
Distribution Made to Limited Partner [Line Items]
Fair Value	$ 1,179,715	$ 1,114,078
New GM Common Stock [Member]
Distribution Made to Limited Partner [Line Items]
Number	15,249,101
Fair Value	553,542
New GM Series A Warrants [Member]
Distribution Made to Limited Partner [Line Items]
Number	13,862,577
Fair Value	368,883
New GM Series B Warrants [Member]
Distribution Made to Limited Partner [Line Items]
Number	13,862,577
Fair Value	$ 257,290