Statements of Consolidated and Combined Comprehensive Income (USD $)
In Millions, unless otherwise specified
 3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Net Income $ 131.2  
Net unrealized gain on cash flow hedges 0.2 [1]  
Other Comprehensive Income, Net of Tax and Transaction Adjustments 0.2  
Total other comprehensive income 0.1 0.3
Total comprehensive income subsequent to IPO 131.4  
Less: Comprehensive income attributable to noncontrolling interest subsequent to IPO 75.3  
Comprehensive income attributable to limited partners subsequent to IPO 13.3  
Predecessor [Member]    
Net Income   92.5
Net unrealized gain on cash flow hedges   0.3 [1]
Total other comprehensive income   0.3
Total comprehensive income subsequent to IPO   $ 92.8
[1] Net unrealized gains on derivatives qualifying as cash flow hedges, net of $0.1 million tax expense in the period prior to the IPO, and $0.2 million tax expense in the first quarter of 2014.