Equity-based Awards, Restricted Unit Awards (Details) - Restricted Common Unit Awards [Member] - USD ($) $ / shares in Units, $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 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)				(1,997,194)
Forfeited (in units)				(157,750)
End of period (in units)		2,074,846		2,074,846
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]			25.99
Forfeited weighted-average grant date fair value per unit (in dollars per unit)	[1]			27.64
Weighted-average grant date fair value per unit, at end of period (in dollars per unit)	[1]	$ 27.85		$ 27.85
Summary of awards activity, equity instruments other than options, additional disclosures [Abstract]
Cash distributions paid to restricted common unitholders		$ 0.8	$ 1.6	$ 3.2	$ 5.7
Total intrinsic value of our restricted common unit awards that vested during period		1.5	$ 1.3	66.9	$ 85.4
Unrecognized Compensation Expense [Abstract]
Unrecognized compensation cost		11.5		$ 11.5
Recognition period for total unrecognized compensation cost				1 year 1 month 6 days
Enterprise [Member]
Unrecognized Compensation Expense [Abstract]
Unrecognized compensation cost		$ 9.6		$ 9.6

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