Reportable Segments (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended	9 Months Ended		3 Months Ended			3 Months Ended					3 Months Ended					3 Months Ended			3 Months Ended		6 Months Ended	9 Months Ended	6 Months Ended	9 Months Ended	6 Months Ended	9 Months Ended	6 Months Ended	9 Months Ended	6 Months Ended	9 Months Ended	3 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2012	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2013 Transportation and Storage [Member]	Sep. 30, 2012 Transportation and Storage [Member]	Dec. 31, 2012 Transportation and Storage [Member]	Sep. 30, 2013 Gathering and Processing [Member]		Sep. 30, 2012 Gathering and Processing [Member]	Dec. 31, 2012 Gathering and Processing [Member]		Sep. 30, 2013 Corporate and other activities [Member]		Sep. 30, 2012 Corporate and other activities [Member]	Dec. 31, 2012 Corporate and other activities [Member]		Sep. 30, 2013 Total segment [Member]	Sep. 30, 2012 Total segment [Member]	Dec. 31, 2012 Total segment [Member]	Sep. 30, 2013 Successor [Member]	Sep. 30, 2012 Successor [Member]	Sep. 30, 2012 Successor [Member]	Sep. 30, 2013 Successor [Member]	Sep. 30, 2012 Successor [Member] Transportation and Storage [Member]	Sep. 30, 2013 Successor [Member] Transportation and Storage [Member]	Sep. 30, 2012 Successor [Member] Gathering and Processing [Member]	Sep. 30, 2013 Successor [Member] Gathering and Processing [Member]	Sep. 30, 2012 Successor [Member] Corporate and other activities [Member]	Sep. 30, 2013 Successor [Member] Corporate and other activities [Member]	Sep. 30, 2012 Successor [Member] Total segment [Member]	Sep. 30, 2013 Successor [Member] Total segment [Member]	Mar. 25, 2012 Predecessor [Member]	Mar. 25, 2012 Predecessor [Member] Transportation and Storage [Member]	Mar. 25, 2012 Predecessor [Member] Gathering and Processing [Member]	Mar. 25, 2012 Predecessor [Member] Corporate and other activities [Member]	Mar. 25, 2012 Predecessor [Member] Total segment [Member]
Segment Reporting Information [Line Items]
Operating revenues from external customers	$ 182	$ 404				$ 180	$ 188		$ 0		$ 213			$ 2		$ 3			$ 180	$ 401				$ 822	$ 891	$ 387	$ 611	$ 430	$ 271	$ 5	$ 9	$ 817	$ 882	$ 443	$ 194	$ 246	$ 3	$ 440
Segment Adjusted EBITDA	153	169				114	119		0		25			39		25								275	522	198	407	36	(7)	41	122			226	186	25	15
Depreciation and amortization	(41)	(67)																				(41)	(67)	(137)	(147)									(49)
Interest expense	(39)	(34)																				(39)	(34)	(95)	(84)									(50)
Net gain on curtailment of OPEB plans			15																					15	0									0
Non-cash equity-based compensation, accretion expense and amortization of regulatory assets	(3)	0																						(1)	(7)									(1)
Other, net	3	(1)																				3	(1)	0	2									(2)
Earnings from unconsolidated investments	9	(1)	0	15																		9	(1)	0	15									16
Adjusted EBITDA attributable to unconsolidated investments	(30)	(4)																						(8)	(56)									(61)
Adjusted EBITDA attributable to discontinued operations	(12)	(23)																						(52)	(75)									(34)
Income from continuing operations before income tax expense	40	39																				40	39	(3)	170									45
Total assets	$ 8,666			$ 8,666	$ 9,993	$ 6,152		$ 6,219	$ 0	[1]		$ 1,965	[1]	$ 2,514	[2]		$ 1,809	[2]	$ 6,152		$ 8,184

[1] (1) The Gathering and Processing segment was contributed to Regency on April 30, 2013. See Note 2.

[2] (2) Corporate and other activities includes the assets of NEG, which have been reported as assets held for sale in the condensed consolidated balance sheets at September 30, 2013 and December 31, 2012. MGE is also included in the balance at December 31, 2012.