Holdings of New GM Securities - Securities Pending Distribution or Set Aside (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Distribution Made to Limited Partner [Line Items]
Fair Value	$ 629,771	$ 464,386
New GM Common Stock [Member]
Distribution Made to Limited Partner [Line Items]
Number	8,647,320	8,380,831
Fair Value	297,641	233,155
New GM Series A Warrants [Member]
Distribution Made to Limited Partner [Line Items]
Number	7,861,059	7,618,851
Fair Value	195,269	141,405
New GM Series B Warrants [Member]
Distribution Made to Limited Partner [Line Items]
Number	7,861,059	7,618,851
Fair Value	$ 136,861	$ 89,826