Holdings of New GM Securities (Details 1) (USD $) In Thousands, except Share data, unless otherwise specified	Mar. 31, 2013	Mar. 31, 2012
New GM Securities Pending Distribution or Set Aside
Fair Value	$ 464,386	$ 168,700
New GM Common Stock [Member]
New GM Securities Pending Distribution or Set Aside
Number	8,380,831	3,311,164
Fair Value	233,155	84,931
New GM Series A Warrants [Member]
New GM Securities Pending Distribution or Set Aside
Number	7,618,851	3,010,012
Fair Value	141,405	50,057
New GM Series B Warrants [Member]
New GM Securities Pending Distribution or Set Aside
Number	7,618,851	3,010,012
Fair Value	$ 89,826	$ 33,712