Quarterly Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended					12 Months Ended		0 Months Ended	3 Months Ended			9 Months Ended
	Mar. 25, 2012 Predecessor [Member]	Dec. 31, 2011 Predecessor [Member]	Sep. 30, 2011 Predecessor [Member]	Jun. 30, 2011 Predecessor [Member]	Mar. 31, 2011 Predecessor [Member]	Dec. 31, 2011 Predecessor [Member]	Dec. 31, 2010 Predecessor [Member]	Mar. 31, 2012 Successor [Member]	Dec. 31, 2012 Successor [Member]	Sep. 30, 2012 Successor [Member]	Jun. 30, 2012 Successor [Member]	Dec. 31, 2012 Successor [Member]
Operating revenues	$ 443	$ 508	$ 536	$ 523	$ 430	$ 1,997	$ 1,789	$ 31	$ 441	$ 405	$ 386	$ 1,263
Operating Income (Loss)	81	112	105	112	84	413	387	(47)	94	73	66	186
Income (Loss) from Continuing Operations	33	61	53	56	44	214	198	(39)	35	12	3	11
Income (Loss) from Discontinued Operations	$ 17	$ 17	$ 5	$ 3	$ 16	$ 41	$ 27	$ 1	$ 14	$ 5	$ 8	$ 28