Acquisitions (Narrative) (Detail) (USD $) In Millions, except Share data, unless otherwise specified	1 Months Ended		3 Months Ended			9 Months Ended												1 Months Ended	3 Months Ended			9 Months Ended			12 Months Ended						1 Months Ended			1 Months Ended	3 Months Ended		9 Months Ended			1 Months Ended						9 Months Ended
	Jul. 02, 2012	Mar. 30, 2012	Sep. 30, 2012	Sep. 30, 2011		Sep. 30, 2012		Sep. 30, 2011		Mar. 13, 2012	Sep. 30, 2010	Sep. 30, 2012 Senior Notes, 4.95% Due 2022 [Member]	Mar. 31, 2012 Senior Notes, 4.95% Due 2022 [Member]	Mar. 13, 2012 Senior Notes, 4.95% Due 2022 [Member]	Jan. 03, 2012 Senior Notes, 4.95% Due 2022 [Member]	Jul. 02, 2012 Mont Belvieu Enterprise Fractionator [Member]	Jul. 02, 2012 Mont Belvieu 1 Fractionator [Member]	Mar. 30, 2012 Southeast Texas [Member]	Sep. 30, 2012 Southeast Texas [Member]	Sep. 30, 2011 Southeast Texas [Member]		Sep. 30, 2012 Southeast Texas [Member]	Sep. 30, 2011 Southeast Texas [Member]		Dec. 31, 2011 Southeast Texas [Member]	Mar. 31, 2012 Southeast Texas [Member]	Jan. 31, 2011 Southeast Texas [Member]	Mar. 31, 2012 Southeast Texas [Member] Senior Notes, 4.95% Due 2022 [Member]	Mar. 30, 2012 Southeast Texas [Member] Termination of Fee Based Storage Arrangement [Member]	Mar. 30, 2012 Southeast Texas [Member] Mitigate Gathering and Processing Commodity Price Risk [Member]	Jan. 03, 2012 East Texas System [Member]	Sep. 30, 2012 East Texas System [Member]	Jan. 31, 2012 East Texas System [Member]	Jul. 03, 2012 Crossroads System [Member] MMcf	Sep. 30, 2012 Crossroads System [Member]	Sep. 30, 2011 Crossroads System [Member]	Sep. 30, 2012 Crossroads System [Member]		Sep. 30, 2011 Crossroads System [Member]	Jul. 03, 2012 Crossroads System [Member] Gas Gathering Pipeline [Member] mi	Jul. 03, 2012 Crossroads System [Member] Ngl Pipeline [Member] mi	Jul. 03, 2012 Crossroads System [Member] Residue Gas Pipeline [Member] mi	Apr. 12, 2012 Texas Express [Member] mi in bbl	Apr. 12, 2012 Texas Express [Member] DCP Midstream, LLC [Member] bbl	Apr. 12, 2012 Texas Express [Member] Long Term Commitments [Member] bbl	Sep. 30, 2012 Eliminations [Member]
Business Acquisition [Line Items]
Aggregate consideration for acquisition	$ 200.0																	$ 240.0													$ 165.0			$ 63.0	$ 63.0		$ 63.0
Pipeline length																																								8	20	11	580
Cryogenic processing plant																																		80
Ownership interest acquired																			66.67%			66.67%				66.67%	33.33%	66.67%			49.90%	49.90%	49.90%									50.00%	10.00%
Total operating revenues			330.9	593.6	[1]	1,270.2	[2]	1,803.1	[3]											210.3	[4]		620.5	[4]											8.5	28.0	27.0	[5]	91.3							5.4
Net income attributable to partners			1.3	68.5	[1]	103.7	[2]	116.2	[3]											5.3	[4]		25.8	[4]											0.8	0.7	1.6	[5]	3.4
Remaining consideration financed through issuance of common units, value	60.0																	48.0													33.0
Issuance of common units	1,536,098	1,000,417																1,000,417													727,520
Minority interests ownership percentage																12.50%	20.00%			33.33%			33.33%		33.33%		33.33%
Term loan	140.0
Excess purchase price over acquired assets	170.2
Business acquisition, portion of purchase price paid in cash																		192.0													132.0												10.9
Aggregate expected consideration for acquisition																																											85.0
Committed Construction Costs																																											75.0
Pipeline diameter in inches																																											20
Pipeline initial capacity																																											280	20	252
Net working capital and other adjustments																		20.7
Senior notes interest rate percentage										4.95%	3.25%	4.95%	4.95%	4.95%	4.95%
Derivatives purchased in an acquisition																		39.5											24.6	14.9
Deficit purchase price																		8.9													22.7
Ownership interest percentage in subsidiary																			100.00%			100.00%	100.00%		100.00%
Ownership interest percentage by parent																															50.10%
Customary purchase price adjustments																															2.5
Aggregate purchase price																															$ 162.5

[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] Adjustments to present Southeast Texas on a consolidated basis at 100% ownership, including commodity derivatives.

[5] The nine months ended September 30, 2012, includes the financial results of Crossroads for the period from January 1, 2012 through July 2, 2012.