Net Income Per Limited Partner Unit - Schedule of Basic and Diluted Net Income Per Unit (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015		Sep. 30, 2016	Sep. 30, 2015
Distribution Made To Limited Partner [Line Items]
Distribution declared	$ 53.9	$ 30.3		$ 144.6	$ 82.1
Income in excess of distributions	2.4	24.0		30.8	28.0
Net income attributable to the Partnership	56.3	54.3	[1]	175.4	110.1	[1]
General Partner
Distribution Made To Limited Partner [Line Items]
Distribution declared	7.1	1.0		14.7	2.1
Income in excess of distributions	0.1	0.5		0.6	0.6
Net income attributable to the Partnership	7.2	1.5		15.3	2.7
Limited Partners' Common Units
Distribution Made To Limited Partner [Line Items]
Distribution declared	29.0	15.4		79.4	41.5
Income in excess of distributions	1.4	12.4		18.0	14.5
Net income attributable to the Partnership	$ 30.4	$ 27.8		$ 97.4	$ 56.0
Weighted average units outstanding
Weighted average unit outstanding, basic and diluted (in shares)	109.8	75.2		99.2	72.6
Net income per limited partner unit
Net income per Limited Partner Unit (in dollars per share)	$ 0.28	$ 0.37	[1]	$ 0.98	$ 0.77	[1]
Limited Partner's Subordinated Units
Distribution Made To Limited Partner [Line Items]
Distribution declared	$ 17.8	$ 13.9		$ 50.5	$ 38.5
Income in excess of distributions	0.9	11.1		12.2	12.9
Net income attributable to the Partnership	$ 18.7	$ 25.0		$ 62.7	$ 51.4
Weighted average units outstanding
Weighted average unit outstanding, basic and diluted (in shares)	67.5	67.5		67.5	67.5
Net income per limited partner unit
Net income per Limited Partner Unit (in dollars per share)	$ 0.28	$ 0.37	[1]	$ 0.93	$ 0.77	[1]

[1] (1) The 2015 financial information has been retrospectively adjusted for the acquisition of the Shell Auger and Lockport Operations.