QUARTERLY OPERATIONS Quarterly Operations (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	Dec. 31, 2011 Predecessor	Sep. 30, 2011 Predecessor	Jun. 30, 2011 Predecessor	Mar. 31, 2011 Predecessor	Dec. 31, 2011 Predecessor	Dec. 31, 2010 Predecessor	Mar. 31, 2013 Successor	Dec. 31, 2012 Successor	Sep. 30, 2012 Successor	Jun. 30, 2012 Successor	Dec. 31, 2012 Successor
Operating revenues	$ 194	$ 219	$ 193	$ 190	$ 202	$ 804	$ 769	$ 13	$ 205	$ 189	$ 185	$ 592
Operating income	88	101	82	88	91	362	339	(26)	89	77	65	205
Net income	$ 40	$ 47	$ 35	$ 40	$ 46	$ 168	$ 148	$ (19)	$ 40	$ 37	$ 30	$ 88