Benefits - Components of Net Periodic Benefit Cost (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended	9 Months Ended		3 Months Ended	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2012 Successor		Mar. 25, 2012 Predecessor	Dec. 31, 2011 Predecessor	Dec. 31, 2010 Predecessor
Defined Benefit Plan Disclosure
Service cost		$ 0		$ 1	$ 2	$ 3
Interest cost		1		1	4	4
Expected return on plan assets		(3)		(1)	(3)	(3)
Prior service credit amortization		0		(1)	(2)	(2)
Curtailment recognition (1)	11	(11)	[1]	0	0	0
Net periodic benefit cost		(13)		0	1	2
Pretax curtailment gain	70
Noncurrent refund liability	$ 59

[1] Subsequent to the Merger, the Company amended certain of its other postretirement employee benefit plans to prospectively restrict participation in the plans for certain active employees. The plan amendments resulted in the plans becoming currently over-funded and, accordingly, the Company recorded a gross pre-tax curtailment gain of $70 million, $59 million of which is subject to refund to customers; thus, the net curtailment gain recognition was $11 million.