CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN PARTNERS' CAPITAL (Unaudited) (USD $) In Millions, unless otherwise specified	Total	Predecessor Equity [Member]	Accumulated Other Comprehensive Loss [Member]	Common Units [Member]	Class B Units [Member]	General Partner [Member]
Beg Partners' Capital, Including Portion Attributable to Noncontrolling Interest at Dec. 31, 2011	$ 3,487.0	$ 281.6	$ (49.4)	$ 2,514.1	$ 678.7	$ 62.0
Adjustments to Partners' Capital [Abstract]
Net Income	92.6	0.2	0	77.0	6.8	8.6
Distributions paid	(114.0)	0	0	(98.1)	(6.8)	(9.1)
Sale of common units, net of related transaction costs	245.0	0	0	245.0	0	0
Capital contribution from general partner	5.2	0	0	0	0	5.2
Predecessor equity carrying amount of acquired entities	(281.8)	(281.8)	0	0	0	0
Excess purchase price over net acquired assets	(3.0)	0	0	(2.6)	(0.3)	(0.1)
Other comprehensive loss	(0.7)	0	(0.7)	0	0	0
End Partners' Capital, Including Portion Attributable to Noncontrolling Interest at Mar. 31, 2012	3,430.3	0	(50.1)	2,735.4	678.4	66.6
Beg Partners' Capital, Including Portion Attributable to Noncontrolling Interest at Dec. 31, 2012	3,877.1	0	(67.3)	3,190.3	678.3	75.8
Adjustments to Partners' Capital [Abstract]
Net Income	101.4	0	0	84.5	6.9	10.0
Distributions paid	(128.3)	0	0	(110.6)	(6.9)	(10.8)
Other comprehensive loss	(6.1)	0	(6.1)	0	0	0
End Partners' Capital, Including Portion Attributable to Noncontrolling Interest at Mar. 31, 2013	$ 3,844.1	$ 0	$ (73.4)	$ 3,164.2	$ 678.3	$ 75.0