Holdings of New GM Securities - Securities Pending Distribution or Set Aside (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	Sep. 30, 2013
Distribution Made to Limited Partner [Line Items]
Fair Value	$ 740,933
New GM Common Stock [Member]
Distribution Made to Limited Partner [Line Items]
Number	9,635,402
Fair Value	346,585
New GM Series A Warrants [Member]
Distribution Made to Limited Partner [Line Items]
Number	8,759,384
Fair Value	231,423
New GM Series B Warrants [Member]
Distribution Made to Limited Partner [Line Items]
Number	8,759,384
Fair Value	$ 162,925