Comprehensive Income (Loss) - Tax amounts in other comprehensive income (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended	12 Months Ended		3 Months Ended
	Dec. 31, 2012	Dec. 31, 2014	Dec. 31, 2013	Mar. 25, 2012
Successor
Income taxes included in other comprehensive income:
Change in fair value of commodity hedges	$ 0	$ 0	$ 0
Reclassification of unrealized loss on interest rate hedges into earnings	0	0	0
Other Comprehensive Income Loss Commodity Hedges Tax	(2)	0	0
Other Comprehensive Income Loss Reclassification Commodity Hedges Tax	0	0	0
Actuarial loss relating to postretirement benefits	(13)	1	(15)
Reclassification of net actuarial loss and prior service credit relating to pension and other postretirement benefits into earnings	0	0	0
Income tax benefit included in other comprehensive income	(15)	1	(15)
Predecessor
Income taxes included in other comprehensive income:
Change in fair value of commodity hedges				2
Reclassification of unrealized loss on interest rate hedges into earnings				3
Other Comprehensive Income Loss Commodity Hedges Tax				2
Other Comprehensive Income Loss Reclassification Commodity Hedges Tax				(1)
Actuarial loss relating to postretirement benefits				0
Reclassification of net actuarial loss and prior service credit relating to pension and other postretirement benefits into earnings				1
Income tax benefit included in other comprehensive income				$ 7