Statements of Consolidated and Combined Comprehensive Income - USD ($)
$ in Millions
 1 Months Ended 3 Months Ended 8 Months Ended 9 Months Ended
Feb. 11, 2015
Sep. 30, 2015
Sep. 30, 2014
Sep. 30, 2015
Sep. 30, 2015
Sep. 30, 2014
Net Income $ 42.7 $ 144.6   $ 340.9 $ 383.6  
Net unrealized gain on cash flow hedges [1]   0.4     1.0  
Unrecognized pension and OPEB costs [2]   (0.2)     (0.2)  
Other Comprehensive Income, Net of Tax and Transaction Adjustments   0.2     0.8  
Total other comprehensive income 0.1 0.2 [3]   0.7   $ 0.8 [3]
Total comprehensive income subsequent to IPO $ 42.8 144.8   341.6 $ 384.4  
Less: Comprehensive income attributable to noncontrolling interest subsequent to IPO   122.8   289.9    
Comprehensive income attributable to limited partners subsequent to IPO   $ 22.0   $ 51.7    
Predecessor            
Net Income     $ 53.2     204.7
Net unrealized gain on cash flow hedges [1]     0.3     0.8
Unrecognized pension and OPEB costs [2]     0.0     0.0
Total other comprehensive income [3]     0.3     0.8
Total comprehensive income subsequent to IPO     $ 53.5     $ 205.5
[1] Net unrealized gains on derivatives qualifying as cash flow hedges, net of zero and $0.2 million tax expense in the third quarter of 2015 and 2014, respectively, and $0.1 million and $0.5 million tax expense for the nine months ended September 30, 2015 and 2014, respectively.
[2] Unrecognized pension and other postretirement benefit (“OPEB”) costs, net of zero tax expense in the third quarter of 2015 and 2014, and zero tax expense for the nine months ended September 30, 2015 and 2014.
[3] All amounts prior to the IPO are net of tax. Amounts in parentheses indicate debits.