Holdings of New GM Securities (Details) (USD $) In Thousands, except Share data, unless otherwise specified	Jun. 30, 2012	Mar. 31, 2012
Schedule of New GM Holding Securities
Fair Value	$ 1,068,464	$ 1,530,262
New GM Common Stock [Member]
Schedule of New GM Holding Securities
Number	29,759,760
Fair Value	586,862
New GM Series A Warrants [Member]
Schedule of New GM Holding Securities
Number	27,054,137
Fair Value	298,175
New GM Series B Warrants [Member]
Schedule of New GM Holding Securities
Number	27,054,137
Fair Value	$ 183,427