Equity-based Awards, Restricted Unit Awards (Details) (Restricted Common Unit Awards [Member], USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
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)	3,893,486		3,868,216		3,561,614
Granted (in units)	1,774,526	[1]	1,588,738	[2]	1,414,630	[3]
Vested (in units)	(1,885,348)		(1,316,603)		(924,108)
Forfeited (in units)	(172,057)		(246,865)		(183,920)
End of period (in units)	3,610,607		3,893,486		3,868,216
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)	$ 40.87	[4]	$ 34.22	[4]	$ 29.78	[4]
Granted weighted-average grant date fair value per unit (in dollars per unit)	$ 57.22	[1],[4]	$ 51.96	[2],[4]	$ 43.66	[3],[4]
Vested weighted-average grant date fair value per unit (in dollars per unit)	$ 34.97	[4]	$ 34.80	[4]	$ 31.54	[4]
Forfeited weighted-average grant date fair value per unit (in dollars per unit)	$ 47.63	[4]	$ 40.43	[4]	$ 34.27	[4]
Weighted-average grant date fair value per unit, at end of period (in dollars per unit)	$ 51.66	[4]	$ 40.87	[4]	$ 34.22	[4]
Summary of awards activity, equity instruments other than options, additional disclosures [Abstract]
Aggregate grant date fair value	$ 101.5		$ 82.5		$ 61.8
Estimated forfeiture rate (in hundredths)	3.90%		3.25%		4.60%
Cash distributions paid to restricted common unitholders	10.6		10.5		9.6
Total intrinsic value of our restricted common unit awards that vested during period	109.9		67.0		39.1
Unrecognized Compensation Expense [Abstract]
Unrecognized compensation cost	72.8
Recognition period for total unrecognized compensation cost	1 year 10 months 24 days
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)	$ 57.11		$ 51.92		$ 40.54
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)	$ 63.48		$ 53.54		$ 44.67
Enterprise [Member]
Unrecognized Compensation Expense [Abstract]
Unrecognized compensation cost	$ 66.2

[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 $57.11 to $63.48 per unit. An estimated annual forfeiture rate of 3.9% was applied to these awards.

[2] The aggregate grant date fair value of restricted common unit awards issued during 2012 was $82.5 million based on a grant date market price of our common units ranging from $51.92 to $53.54 per unit. An estimated annual forfeiture rate of 3.25% was applied to these awards.

[3] The aggregate grant date fair value of restricted common unit awards issued during 2011 was $61.8 million based on a grant date market price of our common units ranging from $40.54 to $44.67 per unit. An estimated annual forfeiture rate of 4.6% was applied to these awards.

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