CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN PARTNERS' CAPITAL (Unaudited) (USD $) In Millions, unless otherwise specified	Total	Predecessor Equity [Member]	Accumulated Other Comprehensive Loss [Member]	Noncontrolling Interest [Member]	Common Units [Member]	Class B Units [Member]	General Partner [Member]
Beg Partners' Capital at Dec. 31, 2011	$ 3,487.0	$ 281.6	$ (49.4)	$ 0	$ 2,514.1	$ 678.7	$ 62.0
Adjustments to Partners' Capital [Abstract]
Net Income	157.7	0.2	0	0	126.7	13.7	17.1
Distributions paid	(228.9)	0	0	0	(196.5)	(13.7)	(18.7)
Sale of common units, net of related transactions costs	245.0	0	0	0	245.0	0	0
Capital contributions from general partner	5.2	0	0	0	0	0	5.2
Predecessor equity carrying amount of acquired entities	(281.8)	(281.8)	0	0	0	0	0
Excess purchase price over net acquired assets	(3.0)	0	0	0	(2.6)	(0.3)	(0.1)
Other comprehensive loss	(9.6)	0	(9.6)	0	0	0	0
End Partners' Capital at Jun. 30, 2012	3,371.6	0	(59.0)	0	2,686.7	678.4	65.5
Beg Partners' Capital at Dec. 31, 2012	3,877.1	0	(67.3)	0	3,190.3	678.3	75.8
Adjustments to Partners' Capital [Abstract]
Net Income	171.8	0	0	(0.1)	138.7	13.7	19.5
Distributions paid	(256.4)	0	0	0	(221.2)	(13.7)	(21.5)
Sale of common units, net of related transactions costs	368.7	0	0	0	368.7	0	0
Capital contributions from general partner	7.8	0	0	0	0	0	7.8
Capital contributions from noncontrolling interests	20.4	0	0	20.4	0	0	0
End Partners' Capital at Jun. 30, 2013	$ 4,189.4	$ 0	$ (67.3)	$ 20.3	$ 3,476.5	$ 678.3	$ 81.6