Holdings of New GM Securities (Details) (USD $) In Thousands, except Share data, unless otherwise specified	Mar. 31, 2013	Mar. 31, 2012
Schedule of New GM Holding Securities
Fair Value	$ 1,591,110	$ 1,530,262
New GM Common Stock [Member]
Schedule of New GM Holding Securities
Number	28,714,897	30,034,667
Fair Value	798,849	770,389
New GM Series A Warrants [Member]
Schedule of New GM Holding Securities
Number	26,104,257	27,304,086
Fair Value	484,492	454,067
New GM Series B Warrants [Member]
Schedule of New GM Holding Securities
Number	26,104,257	27,304,086
Fair Value	$ 307,769	$ 305,806