Equity-based Awards, Phantom Unit Awards (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Summary of awards activity, equity instruments other than options, additional disclosures [Abstract]
Cash payments made in connection with DERs				$ 5.6	$ 2.4
Phantom Unit Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting rate of phantom unit awards (in hundredths)		25.00%		25.00%
Summary of awards activity, equity instruments other than options [Roll Forward]
Beginning of period (in units)				3,342,390
Granted (in units)	[1]			3,491,040
Vested (in units)				(933,890)
Forfeited (in units)				(275,356)
End of period (in units)		5,624,184		5,624,184
Phantom 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)	[2]			$ 33.13
Granted weighted-average grant date fair value per unit (in dollars per unit)	[1],[2]			33.97
Vested weighted-average grant date fair value per unit (in dollars per unit)	[2]			33.13
Forfeited weighted-average grant date fair value per unit (in dollars per unit)	[2]			33.51
Weighted-average grant date fair value per unit, at end of period (in dollars per unit)	[2]	$ 33.63		$ 33.63
Summary of awards activity, equity instruments other than options, additional disclosures [Abstract]
Aggregate grant date fair value				$ 118.6
Estimated forfeiture rate (in hundredths)				3.50%
Cash payments made in connection with DERs		$ 2.2	$ 1.2	$ 5.6	2.4
Total intrinsic value of phantom unit awards that vested during period		2.3	$ 0.1	31.0	$ 1.3
Unrecognized Compensation Expense [Abstract]
Unrecognized compensation cost		100.4		$ 100.4
Recognition period for total unrecognized compensation cost				2 years
Phantom Unit Awards [Member] | Minimum [Member]
Summary of awards activity, equity instruments other than options, additional disclosures [Abstract]
Grant date market price of common units (in dollars per unit)				$ 27.31
Phantom Unit Awards [Member] | Maximum [Member]
Summary of awards activity, equity instruments other than options, additional disclosures [Abstract]
Grant date market price of common units (in dollars per unit)				$ 34.40
Phantom Unit Awards [Member] | Enterprise [Member]
Unrecognized Compensation Expense [Abstract]
Unrecognized compensation cost		$ 91.7		$ 91.7

[1] The aggregate grant date fair value of phantom unit awards issued during 2015 was $118.6 million based on a grant date market price of our common units ranging from $27.31 to $34.40 per unit. An estimated annual forfeiture rate of 3.5% was applied to these awards.

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