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Equity-based Awards, Restricted Unit Awards (Details) (Restricted Common Unit Awards [Member], USD $)
In Millions, except Share data, unless otherwise specified
 3 Months Ended
Mar. 31, 2014
Mar. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Vesting rate of restricted common unit awards (in hundredths) 25.00%  
Summary of awards activity, equity instruments other than options [Roll Forward]    
Beginning of period (in units) 3,610,607  
Vested (in units) (1,239,862)  
Forfeited (in units) (86,650)  
End of period (in units) 2,284,095  
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) $ 51.66 [1]  
Vested weighted-average grant date fair value per unit (in dollars per unit) $ 47.71 [1]  
Forfeited weighted-average grant date fair value per unit (in dollars per unit) $ 51.89 [1]  
Weighted-average grant date fair value per unit, at end of period (in dollars per unit) $ 53.80 [1]  
Summary of awards activity, equity instruments other than options, additional disclosures [Abstract]    
Cash distributions paid to restricted common unitholders $ 2.5 $ 2.6
Total intrinsic value of our restricted common unit awards that vested during period 81.4 52.4
Unrecognized Compensation Expense [Abstract]    
Unrecognized compensation cost 57.3  
Recognition period for total unrecognized compensation cost 1 year 10 months 24 days  
Enterprise [Member]
    
Unrecognized Compensation Expense [Abstract]    
Unrecognized compensation cost $ 51.7  
[1] Determined by dividing the aggregate grant date fair value of awards (before an allowance for forfeitures) by the number of awards issued.