Partnership Equity And Distributions (Narrative) (Detail) (USD $) In Millions, except Share data, unless otherwise specified	0 Months Ended	1 Months Ended		9 Months Ended							3 Months Ended	9 Months Ended		1 Months Ended	9 Months Ended				1 Months Ended				1 Months Ended			9 Months Ended
	Jul. 02, 2012	Jul. 02, 2012	Mar. 30, 2012	Sep. 30, 2012 D		Sep. 30, 2011		Mar. 31, 2012	Feb. 29, 2012	Dec. 31, 2011	Sep. 30, 2012 Equity Distribution Agreement [Member]	Sep. 30, 2012 Equity Distribution Agreement [Member]	Aug. 30, 2011 Equity Distribution Agreement [Member]	Jul. 31, 2012 Mont Belvieu Fractionators [Member]	Sep. 30, 2012 Distribution Stage First [Member]	Sep. 30, 2012 Distribution Stage Second [Member]	Sep. 30, 2012 Distribution Stage Third [Member]	Sep. 30, 2012 Distribution Stage Thereafter [Member]	Mar. 30, 2012 Southeast Texas [Member]	Sep. 30, 2012 Southeast Texas [Member]	Mar. 31, 2012 Southeast Texas [Member]	Jan. 31, 2011 Southeast Texas [Member]	Jan. 03, 2012 East Texas System [Member]	Sep. 30, 2012 East Texas System [Member]	Jan. 31, 2012 East Texas System [Member]	Sep. 30, 2012 General Partner [Member]
Partnership Equity And Distribution [Line Items]
Partnership deadline for distributions (in days)				45
Consideration financed through issuance of common units		1,536,098	1,000,417											1,536,098					1,000,417				727,520
Number of common units sold	4,989,802
Common units sold per unit	$ 35.55
Net proceeds	$ 173.8
Common unitholders, units issued				59,179,130				5,148,500	30,701	44,848,703	893,389	893,389
Common units, per unit								$ 47.42
Net proceeds								234.0
Ownership interest acquired																				66.67%	66.67%	33.33%	49.90%	49.90%	49.90%
Maximum aggregate offering price													150.0
Net proceeds				445.2	[1]	152.0	[2]				23.3	37.4
Commissions and offering costs											$ 0.6	$ 0.9
General partner ownership interest																										1.00%
Limited partner ownership interest																										1.00%
Limited Partner pro rata interest															$ 0.4025	$ 0.4375	$ 0.525
General Partner pro rata interest per unit																13	23	48

[1] 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.

[2] The financial information during 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.