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, 2015		Mar. 31, 2014
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)	4,229,790
Vested (in units)	(1,852,746)
Forfeited (in units)	(84,700)
End of period (in units)	2,292,344
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)	$ 26.96	[1]
Vested weighted-average grant date fair value per unit (in dollars per unit)	$ 25.89	[1]
Forfeited weighted-average grant date fair value per unit (in dollars per unit)	$ 27.16	[1]
Weighted-average grant date fair value per unit, at end of period (in dollars per unit)	$ 27.82	[1]
Summary of awards activity, equity instruments other than options, additional disclosures [Abstract]
Cash distributions paid to restricted common unitholders	$ 1.5		$ 2.5
Total intrinsic value of our restricted common unit awards that vested during period	62.4		81.4
Unrecognized Compensation Expense [Abstract]
Unrecognized compensation cost	20.5
Recognition period for total unrecognized compensation cost	1 year 4 months 24 days
Enterprise [Member]
Unrecognized Compensation Expense [Abstract]
Unrecognized compensation cost	$ 17.7

[1] Determined by dividing the aggregate grant date fair value of awards (before an allowance for forfeitures) by the number of awards issued.