Derivative Instrument and Hedging Activities - Derivative Effects on Income (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended	9 Months Ended	3 Months Ended			6 Months Ended	9 Months Ended	3 Months Ended			6 Months Ended	9 Months Ended	3 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2012 Successor [Member]	Sep. 30, 2013 Successor [Member]	Mar. 25, 2012 Predecessor [Member]	Sep. 30, 2013 Gains (Losses) On Non-Hedged Interest Rate Derivatives [Member] Interest Rate Derivatives [Member]	Sep. 30, 2012 Gains (Losses) On Non-Hedged Interest Rate Derivatives [Member] Interest Rate Derivatives [Member]	Sep. 30, 2012 Gains (Losses) On Non-Hedged Interest Rate Derivatives [Member] Interest Rate Derivatives [Member] Successor [Member]	Sep. 30, 2013 Gains (Losses) On Non-Hedged Interest Rate Derivatives [Member] Interest Rate Derivatives [Member] Successor [Member]	Mar. 25, 2012 Gains (Losses) On Non-Hedged Interest Rate Derivatives [Member] Interest Rate Derivatives [Member] Predecessor [Member]	Sep. 30, 2013 Deferred Gas Purchases [Member] Commodity [Member]	Sep. 30, 2012 Deferred Gas Purchases [Member] Commodity [Member]	Sep. 30, 2012 Deferred Gas Purchases [Member] Commodity [Member] Successor [Member]	Sep. 30, 2013 Deferred Gas Purchases [Member] Commodity [Member] Successor [Member]	Mar. 25, 2012 Deferred Gas Purchases [Member] Commodity [Member] Predecessor [Member]
Cash Flow Hedges: Interest rate contracts:
Change in fair value - increase in Accumulated other comprehensive income			$ 0	$ 0	$ 6
Reclassification of unrealized loss from Accumulated other comprehensive income - increase of Interest expense			0	0	8
Derivative Instruments, Gain (Loss) Recognized in Other Comprehensive Income (Loss), Effective Portion, Net	0	(5)	6	(3)	5
Derivative Instruments, Gain (Loss) Reclassified from Accumulated OCI into Income, Effective Portion, Net	0	6	12	0	2
Economic Hedges: Interest rate contracts: [Abstract]
Derivative Instruments, Gain (Loss) Recognized in Income, Net						$ 1	$ (5)	$ 15	$ (27)	$ 0	$ (4)	$ (11)	$ (31)	$ (7)	$ (2)