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Equity-based Awards, Restricted Unit Awards (Details) - Restricted Common Unit Awards [Member] - Range [Domain] - USD ($)
$ / shares in Units, $ in Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2015
Jun. 30, 2014
Jun. 30, 2015
Jun. 30, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Vesting rate of restricted common unit awards (in hundredths) 25.00%   25.00%  
Summary of awards activity, equity instruments other than options [Roll Forward]        
Beginning of period (in units)     4,229,790  
Vested (in units)     (1,940,044)  
Forfeited (in units)     (111,250)  
End of period (in units) 2,178,496   2,178,496  
Restricted units outstanding, weighted-average grant date fair value [Roll Forward]        
Weighted-average grant date fair value per unit, at beginning of period (in dollars per unit) [1]     $ 26.96  
Vested weighted-average grant date fair value per unit (in dollars per unit) [1]     25.96  
Forfeited weighted-average grant date fair value per unit (in dollars per unit) [1]     27.47  
Weighted-average grant date fair value per unit, at end of period (in dollars per unit) [1] $ 27.83   $ 27.83  
Summary of awards activity, equity instruments other than options, additional disclosures [Abstract]        
Cash distributions paid to restricted common unitholders $ 0.9 $ 1.6 $ 2.4 $ 4.1
Total intrinsic value of our restricted common unit awards that vested during period 3.0 $ 2.7 65.4 $ 84.1
Unrecognized Compensation Expense [Abstract]        
Unrecognized compensation cost 15.9   $ 15.9  
Recognition period for total unrecognized compensation cost     1 year 2 months 12 days  
Enterprise [Member]        
Unrecognized Compensation Expense [Abstract]        
Unrecognized compensation cost $ 13.5   $ 13.5  
[1] Determined by dividing the aggregate grant date fair value of awards (before an allowance for forfeitures) by the number of awards issued.