Holdings of New GM Securities - Holdings of Securities for Trust Beneficiaries (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	Sep. 30, 2013	Mar. 31, 2013
Distribution Made to Limited Partner [Line Items]
Fair Value	$ 2,189,737	$ 1,591,110
New GM Common Stock [Member]
Distribution Made to Limited Partner [Line Items]
Number	28,476,244
Fair Value	1,024,290
New GM Series A Warrants [Member]
Distribution Made to Limited Partner [Line Items]
Number	25,887,311
Fair Value	683,943
New GM Series B Warrants [Member]
Distribution Made to Limited Partner [Line Items]
Number	25,887,311
Fair Value	$ 481,504