Holdings of New GM Securities - Securities Pending Distribution or Set Aside (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	Sep. 30, 2014
Distribution Made to Limited Partner [Line Items]
Fair Value	$ 552,066
New GM Common Stock [Member]
Distribution Made to Limited Partner [Line Items]
Number	8,437,416
Fair Value	269,491
New GM Series A Warrants [Member]
Distribution Made to Limited Partner [Line Items]
Number	7,670,246
Fair Value	171,660
New GM Series B Warrants [Member]
Distribution Made to Limited Partner [Line Items]
Number	7,670,246
Fair Value	$ 110,915