Equity - Schedule of Distributions Declared and/or Paid (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	[1]
Distribution Made To Limited Partner [Line Items]
Date Paid or to be Paid	Nov. 12, 2015	Aug. 13, 2015	May 14, 2015	Feb. 12, 2015
Distributions declared and/or paid	$ 30.3	$ 27.7	$ 24.1	$ 14.4
Distributions paid per limited partner unit		$ 0.1900	$ 0.1750	$ 0.1042
Distributions declared per limited partner unit	$ 0.2050
Common Units
Distribution Made To Limited Partner [Line Items]
Distributions declared and/or paid	$ 11.0	$ 10.2	$ 8.0	$ 4.8
Common Units | SPLC
Distribution Made To Limited Partner [Line Items]
Distributions declared and/or paid	4.4	4.1	3.8	2.2
Subordinate Units | SPLC
Distribution Made To Limited Partner [Line Items]
Distributions declared and/or paid	13.9	12.8	11.8	7.1
General Partner
Distribution Made To Limited Partner [Line Items]
Distributions declared and/or paid	0.6	0.5	$ 0.5	$ 0.3
General Partner | General Partner Incentive
Distribution Made To Limited Partner [Line Items]
Distributions declared and/or paid	$ 0.4	$ 0.1

[1] The fourth quarter 2014 minimum quarterly distribution was prorated for the 59-day period from November 3, 2014 to December 31, 2014 in accordance with the Partnership Agreement.