Equity-Based Awards, Restricted Unit Awards (Details) - Restricted Common Unit Awards [Member] - USD ($) $ / shares in Units, $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 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)		4,229,790	7,221,214	7,786,972
Granted (in units)	[1]			3,549,052
Vested (in units)		(2,009,970)	(2,634,074)	(3,770,696)
Forfeited (in units)		(259,300)	(357,350)	(344,114)
End of period (in units)		1,960,520	4,229,790	7,221,214
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)	[2]	$ 26.96	$ 25.83	$ 20.43
Granted weighted-average grant date fair value per unit (in dollars per unit)	[1],[2]			28.61
Vested weighted-average grant date fair value per unit (in dollars per unit)	[2]	26.00	23.94	17.48
Forfeited weighted-average grant date fair value per unit (in dollars per unit)	[2]	27.53	26.38	23.82
Weighted-average grant date fair value per unit, at end of period (in dollars per unit)	[2]	$ 27.88	$ 26.96	$ 25.83
Summary of awards activity, equity instruments other than options, additional disclosures [Abstract]
Aggregate grant date fair value				$ 101.5
Estimated forfeiture rate (in hundredths)				3.90%
Cash distributions paid to restricted common unitholders		$ 4.0	$ 7.3	$ 10.6
Total intrinsic value of restricted common unit awards that vested during period		67.3	$ 87.1	$ 109.9
Unrecognized Compensation Expense [Abstract]
Unrecognized compensation cost		$ 7.2
Recognition period for total unrecognized compensation cost		1 year
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)				$ 28.56
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)				$ 31.74
Enterprise [Member]
Unrecognized Compensation Expense [Abstract]
Unrecognized compensation cost		$ 5.7

[1] The aggregate grant date fair value of restricted common unit awards issued during 2013 was $101.5 million based on a grant date market price of our common units ranging from $28.56 to $31.74 per unit. An estimated annual forfeiture rate of 3.9% 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.