Holdings of New GM Securities (Details) (USD $) In Thousands, except Share data, unless otherwise specified	Sep. 30, 2012	Mar. 31, 2012
Schedule of New GM Holding Securities
Fair Value	$ 1,251,821	$ 1,530,262
New GM Common Stock [Member]
Schedule of New GM Holding Securities
Number	29,257,588
Fair Value	665,610
New GM Series A Warrants [Member]
Schedule of New GM Holding Securities
Number	26,597,604
Fair Value	366,515
New GM Series B Warrants [Member]
Schedule of New GM Holding Securities
Number	26,597,604
Fair Value	$ 219,696