Derivative Instrument and Hedging Activities - Derivative Effects on Income (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended	3 Months Ended	12 Months Ended
	Dec. 31, 2012 Successor [Member]	Mar. 25, 2012 Predecessor [Member]	Dec. 31, 2011 Predecessor [Member]	Dec. 31, 2010 Predecessor [Member]
Cash Flow Hedges: Interest rate contracts:
Change in fair value - increase in Accumulated other comprehensive income	$ 0	$ 6	$ 74	$ 13
Reclassification of unrealized loss from Accumulated other comprehensive income - increase of Interest expense	0	8	22	22
Cash Flow Hedges: Commodity contracts - Gathering and Processing:
Change in fair value - increase/(decrease) in Accumulated other comprehensive income	(6)	5	(7)	(39)
Reclassification of unrealized gain from Accumulated other comprehensive income	1	2	24	19
Economic Hedges: Interest rate contracts: [Abstract]
Change in fair value - increase in interest expense	12	0	0	0
Economic Hedges: Commodity contracts - Gathering and Processing:
Change in fair value of other hedges - decrease in Operating revenues	0	0	30	31
Economic Hedges: Commodity contracts - Distribution:
Change in fair value - increase/(decrease) in Deferred natural gas purchases	$ (32)	$ (2)	$ 3	$ (6)