Holdings of New GM Securities (Details) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2012	Mar. 31, 2012
Schedule of New GM Holding Securities
Fair Value	$ 1,685,335	$ 1,530,262
New GM Common Stock [Member]
Schedule of New GM Holding Securities
Number	29,101,877
Fair Value	839,007
New GM Series A Warrants [Member]
Schedule of New GM Holding Securities
Number	26,456,021
Fair Value	515,892
New GM Series B Warrants [Member]
Schedule of New GM Holding Securities
Number	26,456,021
Fair Value	$ 330,436