Holdings of New GM Securities - Holdings of Securities for Trust Beneficiaries (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2013	Mar. 31, 2013
Distribution Made to Limited Partner [Line Items]
Fair Value	$ 1,384,305	$ 1,591,110
New GM Common Stock [Member]
Distribution Made to Limited Partner [Line Items]
Number	15,347,633
Fair Value	627,258
New GM Series A Warrants [Member]
Distribution Made to Limited Partner [Line Items]
Number	13,952,218
Fair Value	434,472
New GM Series B Warrants [Member]
Distribution Made to Limited Partner [Line Items]
Number	13,952,218
Fair Value	$ 322,575