Holdings of New GM Securities - Securities Pending Distribution or are Set Aside (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	Mar. 31, 2015	Mar. 31, 2014
Distribution Made to Limited Partner [Line Items]
Fair Value	$ 372,237	$ 629,771
New GM Common Stock [Member]
Distribution Made to Limited Partner [Line Items]
Number	4,618,904	8,647,320
Fair Value	173,209	297,641
New GM Series A Warrants [Member]
Distribution Made to Limited Partner [Line Items]
Number	4,198,901	7,861,059
Fair Value	116,520	195,269
New GM Series B Warrants [Member]
Distribution Made to Limited Partner [Line Items]
Number	4,198,901	7,861,059
Fair Value	$ 82,508	$ 136,861