Income Taxes (Details 2) (USD $)	9 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2012	Mar. 31, 2011 Predecessor	Dec. 31, 2010 Predecessor	Dec. 31, 2012 Alternative minimum tax credits	Dec. 31, 2012 Investment tax credits	Dec. 31, 2012 Investment tax credits State
Income Taxes
NOLs		$ 5,300,000,000
Income taxes
Tax credits					45,000,000		72,000,000
Tax credit carryforwards, net of federal income tax						47,000,000
State deferred tax expense (benefit ), net of federal effect resulting from changes in state tax rate				4,000,000
Income tax paid	13,000,000	(2,000,000)	1,000,000	(25,000,000)
Valuation allowance	256,000,000	260,000,000		139,000,000
Increase in valuation allowance as a result of acquisition accounting		110,000,000
Change in unrecognized tax benefits for uncertain tax positions		$ 25,000,000