Reportable Segments 1 (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended	0 Months Ended	3 Months Ended			9 Months Ended						3 Months Ended					12 Months Ended		3 Months Ended	12 Months Ended		3 Months Ended	12 Months Ended		3 Months Ended	12 Months Ended		3 Months Ended	12 Months Ended		3 Months Ended	12 Months Ended
	Dec. 31, 2012	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]	Dec. 31, 2012 Successor [Member] Transportation and Storage [Member]	Dec. 31, 2012 Successor [Member] Gathering and Processing [Member]	Dec. 31, 2012 Successor [Member] Distribution [Member]	Dec. 31, 2012 Successor [Member] Total segment [Member]	Dec. 31, 2012 Successor [Member] Corporate and other activities [Member]	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. 25, 2012 Predecessor [Member] Transportation and Storage [Member]	Dec. 31, 2011 Predecessor [Member] Transportation and Storage [Member]	Dec. 31, 2010 Predecessor [Member] Transportation and Storage [Member]	Mar. 25, 2012 Predecessor [Member] Gathering and Processing [Member]	Dec. 31, 2011 Predecessor [Member] Gathering and Processing [Member]	Dec. 31, 2010 Predecessor [Member] Gathering and Processing [Member]	Mar. 25, 2012 Predecessor [Member] Distribution [Member]	Dec. 31, 2011 Predecessor [Member] Distribution [Member]	Dec. 31, 2010 Predecessor [Member] Distribution [Member]	Mar. 25, 2012 Predecessor [Member] Total segment [Member]	Dec. 31, 2011 Predecessor [Member] Total segment [Member]	Dec. 31, 2010 Predecessor [Member] Total segment [Member]	Mar. 25, 2012 Predecessor [Member] Corporate and other activities [Member]	Dec. 31, 2011 Predecessor [Member] Corporate and other activities [Member]	Dec. 31, 2010 Predecessor [Member] Corporate and other activities [Member]
Segment Reporting Information [Line Items]
Operating revenues from external customers		$ 31	$ 441	$ 405	$ 386	$ 1,263	$ 592	$ 663		$ 1,255	$ 8	$ 443	$ 508	$ 536	$ 523	$ 430	$ 1,997	$ 1,789	$ 194	$ 804	$ 769	$ 246	$ 1,180	$ 1,008				$ 440	$ 1,984	$ 1,777	$ 3	$ 13	$ 12
Segment Adjusted EBITDA						442	326	40	68		8	226					987	984	186	778	753	25	125	127	34	90	98				(19)	(6)	6
Depreciation and amortization						(179)	(125)	(52)		(177)	(2)	(49)					(204)	(196)	(30)	(128)	(123)	(18)	(73)	(70)				(48)	(201)	(193)	(1)	(3)	(3)
Unrealized gains on unhedged derivative activities						0						0					0	(19)
Net gain on curtailment of OPEB plans	15					15						0					0	0
Non-cash equity-based compensation, accretion expense and amortization of regulatory assets						(4)						(1)					(9)	(8)
Other, net						2						(2)					0	2
Income (Loss) from Equity Method Investments						(7)	1	(8)			0	16					99	105	16	98	100	0	0	4							0	1	1
Proportionate share of unconsolidated investments' interest, depreciation and allowance for equity funds used during construction						(5)						(61)					(262)	(267)
Adjusted EBITDA attributable to discontinued operations						(83)						(34)					(99)	(107)
Interest expense						(131)						(50)					(218)	(216)
Income (Loss) from Continuing Operations before Income Taxes, Domestic						50						45					294	278
Total assets			9,993			9,993	6,219	1,965	1,190	9,374	619		8,271				8,271			5,289			1,743			1,075			8,107			164
Segment Reporting Information, Expenditures for Additions to Long-Lived Assets						$ 340	$ 96	$ 200	$ 44	$ 340	$ 0	$ 75					$ 269	$ 287	$ 23	$ 102	$ 146	$ 42	$ 114	$ 96	$ 9	$ 51	$ 41	$ 74	$ 267	$ 283	$ 1	$ 2	$ 4