Comprehensive Income (Loss) - Tax amounts in other comprehensive income (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended	3 Months Ended	12 Months Ended
	Dec. 31, 2012 Successor	Mar. 25, 2012 Predecessor	Dec. 31, 2011 Predecessor	Dec. 31, 2010 Predecessor
Income taxes included in other comprehensive income:
Reclassification of unrealized loss on interest rate hedges into earnings	$ 0	$ 2	$ 9	$ 9
Change in fair value of interest rate hedges	0	0	(1)	(5)
Actuarial loss relating to postretirement benefits	(6)	0	(6)	0
Reclassification of prior service credit relating to other postretirement benefits into earnings	0	0	(1)	(1)
Income tax benefit included in other comprehensive income	$ (6)	$ 2	$ 1	$ 3