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, 2016
Sep. 30, 2015
Sep. 30, 2015
Sep. 30, 2016
Sep. 30, 2015
Net Income $ 42.7 $ 20.9 $ 144.6 $ 340.9 $ 331.4 $ 383.6
Net unrealized gain on cash flow hedges [1]   0.6 0.4   1.6 1.0
Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Adjustment, Net of Tax [2],[3]   0.1 (0.2)   0.1 (0.2)
Total other comprehensive income   0.7 0.2   1.7 0.8
Other Comprehensive Income (Loss) 0.1 0.7 [4] 0.2 [4] 0.7 1.7 [4] 0.8 [4],[5]
Total comprehensive income subsequent to IPO $ 42.8 21.6 144.8 $ 341.6 333.1 384.4
Less: Comprehensive income attributable to noncontrolling interest subsequent to IPO   18.6 122.8   284.5 289.9
Comprehensive income attributable to limited partners subsequent to IPO   $ 3.0 $ 22.0   $ 48.6 $ 51.7
[1] Net unrealized gains on derivatives qualifying as cash flow hedges, net of zero tax expense for the three months ended September 30, 2016 and 2015, and zero and $0.1 million tax expense for the nine months ended September 30, 2016 and 2015, respectively
[2] Unrecognized pension and OPEB benefit (cost), net of zero tax expense for the three months ended September 30, 2016 and 2015, and zero tax expense for the nine months ended September 30, 2016 and 2015.
[3] Unrecognized pension and OPEB benefits are primarily related to pension and OPEB remeasurements recorded during 2016 and 2015.
[4] Amounts in parentheses indicate debits.
[5] All amounts prior to the IPO are net of tax.