Accumulated Other Comprehensive Loss (Components Of Accumulated Other Comprehensive Loss) (Details) - USD ($)
$ in Millions
 1 Months Ended 11 Months Ended 12 Months Ended
Feb. 11, 2015
Dec. 31, 2015
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Accumulated Other Comprehensive Income (Loss) [Line Items]          
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax [1]     $ (0.3)    
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [1],[2]     1.6    
Total comprehensive income $ 0.1 $ 1.2 1.3 [1]    
Partners Capital Predecessor Net Liabilities Not Assumed By Subsidiary 1,222.2        
Ending Balance [1]   (4.0) (4.0)    
Gains and Losses on Cash Flow Hedges          
Accumulated Other Comprehensive Income (Loss) [Line Items]          
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax [1]     0.0    
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [1],[2]     1.5    
Total comprehensive income [1]     1.5    
Partners Capital Predecessor Net Liabilities Not Assumed By Subsidiary [1],[3]     (10.2)    
Ending Balance [1]   (3.9) (3.9)    
Pension and OPEB Items          
Accumulated Other Comprehensive Income (Loss) [Line Items]          
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax [1]     (0.3)    
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [1],[2]     0.1    
Total comprehensive income [1]     (0.2)    
Partners Capital Predecessor Net Liabilities Not Assumed By Subsidiary [1],[3]     (0.1)    
Ending Balance [1]   (0.1) (0.1)    
Gains and Losses on Cash Flow Hedges Attributable to Noncontrolling Interest          
Accumulated Other Comprehensive Income (Loss) [Line Items]          
Total comprehensive income [1]     (21.4)    
Pension and OPEB Items Attributable to Noncontrolling Interest [Member]          
Accumulated Other Comprehensive Income (Loss) [Line Items]          
Total comprehensive income [1]     (0.3)    
AOCI Attributable to Noncontrolling Interest          
Accumulated Other Comprehensive Income (Loss) [Line Items]          
Total comprehensive income [1]     (21.7)    
Accumulated Other Comprehensive Loss          
Accumulated Other Comprehensive Income (Loss) [Line Items]          
Total comprehensive income 0.1 $ 0.2      
Partners Capital Predecessor Net Liabilities Not Assumed By Subsidiary (10.3)   (10.3) [1],[3]    
Predecessor          
Accumulated Other Comprehensive Income (Loss) [Line Items]          
Beginning Balance [1] (16.7)   (16.7) $ (17.7) $ (18.8)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax [1]       0.0 0.0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [1]       1.0 1.1
Total comprehensive income [1]       1.0 1.1
Ending Balance [1]       (16.7) (17.7)
Predecessor | Gains and Losses on Cash Flow Hedges          
Accumulated Other Comprehensive Income (Loss) [Line Items]          
Beginning Balance [1] (16.6)   (16.6) (17.6) (18.7)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax [1]       0.0 0.0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [1]       1.0 1.1
Total comprehensive income [1]       1.0 1.1
Ending Balance [1]       (16.6) (17.6)
Predecessor | Pension and OPEB Items          
Accumulated Other Comprehensive Income (Loss) [Line Items]          
Beginning Balance [1] $ (0.1)   $ (0.1) (0.1) (0.1)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax [1]       0.0 0.0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax [1]       0.0 0.0
Total comprehensive income [1]       0.0 0.0
Ending Balance [1]       $ (0.1) $ (0.1)
[1] All amounts prior to the IPO are net of tax. Amounts in parentheses indicate debits.
[2] Includes amounts allocated to noncontrolling interest.
[3] Reflects the non-cash elimination of all historical current and deferred income taxes other than Tennessee state income taxes that will continue to be borne by the Partnership post-IPO.