Holdings of New GM Securities (Details) (USD $) In Thousands, except Share data, unless otherwise specified	Jun. 30, 2013	Mar. 31, 2013
Schedule of New GM Holding Securities
Fair Value	$ 1,998,601	$ 1,591,110
New GM Common Stock [Member]
Schedule of New GM Holding Securities
Number	28,554,891
Fair Value	951,164
New GM Series A Warrants [Member]
Schedule of New GM Holding Securities
Number	25,958,804
Fair Value	623,011
New GM Series B Warrants [Member]
Schedule of New GM Holding Securities
Number	25,958,804
Fair Value	$ 424,426