Condensed Consolidated Statements Of Operations (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2012		Sep. 30, 2011
Operating revenues:
Sales of natural gas, propane, NGLs and condensate	$ 305.8		$ 496.1	[1]	$ 1,089.4	[2]	$ 1,652.7	[3]
Transportation, processing and other	45.0		42.8	[1]	130.7	[2]	122.2	[3]
(Losses) gains from commodity derivative activity, net	(19.9)		54.7	[1]	50.1	[2]	28.2	[3]
Total operating revenues	330.9		593.6	[1]	1,270.2	[2]	1,803.1	[3]
Operating costs and expenses:
Purchases of natural gas, propane and NGLs	268.0		449.0	[1]	973.4	[2]	1,464.3	[3]
Operating and maintenance expense	35.7		36.7	[1]	91.7	[2]	91.3	[3]
Depreciation and amortization expense	14.8		25.9	[1]	49.6	[2]	74.9	[3]
General and administrative expense	11.1		12.0	[1]	34.0	[2]	35.2	[3]
Other income	(0.1)		(0.2)	[1]	(0.4)	[2]	(0.4)	[3]
Total operating costs and expenses	329.5		523.4	[1]	1,148.3	[2]	1,665.3	[3]
Operating income	1.4		70.2	[1]	121.9	[2]	137.8	[3]
Interest expense	(8.1)		(8.6)	[1]	(31.8)	[2]	(25.0)	[3]
Earnings from unconsolidated affiliates	8.9		6.9	[1]	16.6	[2]	17.1	[3]
Income before income taxes	2.2		68.5	[1]	106.7	[2]	129.9	[3]
Income tax expense	(0.3)	[4]	(0.4)	[1],[4]	(1.0)	[2],[4]	(0.9)	[3],[4]
Net income	1.9		68.1	[1]	105.7	[2]	129.0	[3]
Net (income) loss attributable to noncontrolling interests	(0.6)		0.4	[1]	(2.0)	[2]	(12.8)	[3]
Net income attributable to partners	1.3		68.5	[1]	103.7	[2]	116.2	[3]
Net income attributable to predecessor operations			(2.2)		(2.6)		(14.3)
General partner's interest in net income	(10.8)		(6.8)		(29.4)		(18.5)
Net (loss) income allocable to limited partners	(9.5)		59.5		71.7		83.4
Net (loss) income per limited partner unit - basic	(0.16)		1.35		1.37		1.93
Net (loss) income per limited partner unit - diluted	(0.16)		1.35		1.36		1.93
Weighted-average limited partner units outstanding - basic	58.7		44.1		52.5		43.2
Weighted-average limited partner units outstanding - diluted	58.7		44.2		52.6		43.2
Third Party [Member]
Operating revenues:
Sales of natural gas, propane, NGLs and condensate	144.4		227.8		540.3		801.7
Transportation, processing and other	36.2		33.1		102.5		99.2
(Losses) gains from commodity derivative activity, net	(11.1)		54.1		17.0		29.0
Operating costs and expenses:
Purchases of natural gas, propane and NGLs	247.9		372.0		761.0		1,150.3
General and administrative expense	3.7		4.7		11.9		13.2
Affiliated Entity [Member]
Operating revenues:
Sales of natural gas, propane, NGLs and condensate	161.4		268.3		549.1		851.0
Transportation, processing and other	8.8		9.7		28.2		23.0
(Losses) gains from commodity derivative activity, net	(8.8)		0.6		33.1		(0.8)
Operating costs and expenses:
Purchases of natural gas, propane and NGLs	20.1		77.0		212.4		314.0
General and administrative expense	$ 7.4		$ 7.3		$ 22.1		$ 22.0

[1] The financial information for the three months ended September 30, 2011 includes the results of Southeast Texas, a transfer of net assets between entities under common control that was accounted for as if the transfer occurred at the beginning of the period, and prior years are retrospectively adjusted to furnish comparative information similar to the pooling method.

[2] The financial information for the nine months ended September 30, 2012 includes the results of Southeast Texas, a transfer of net assets between entities under common control that was accounted for as if the transfer occurred at the beginning of the period, and prior years are retrospectively adjusted to furnish comparative information similar to the pooling method.

[3] The financial information for the nine months ended September 30, 2011 includes the results of Southeast Texas, a transfer of net assets between entities under common control that was accounted for as if the transfer occurred at the beginning of the period, and prior years are retrospectively adjusted to furnish comparative information similar to the pooling method.

[4] For the three and nine months ended September 30, 2011, income tax expense relates primarily to the Texas margin tax and the Michigan business tax. The Michigan business tax was repealed in 2012; accordingly, income tax expense for the three and nine months ended September 30, 2012 relates primarily to the Texas margin tax.