Equity and Distributions, Summary of Changes in Outstanding Units (Details)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Common Units (Unrestricted) [Member]
Summary of changes in outstanding units [Roll Forward]
Beginning Balance (in units)	894,919,851	877,752,202	840,119,958
Common units issued in connection with underwritten offerings (in units)	18,400,000	9,200,000	10,350,000
Common units issued in connection with at-the-market program (in units)	7,624,689	3,978,545
Common units issued in connection with Duncan Merger (in units)			24,277,310
Common units issued in connection with DRIP and EUPP (in units)	5,154,127	2,814,660	2,337,904
Common units issued in connection with the vesting of unit options (in units)	200,882	213,914
Common units issued in connection with the vesting of restricted common unit awards (in units)	1,885,348	1,316,603	924,108
Common units issued in connection with the vesting of other types of equity-based awards (in units)		52,168
Conversion and reclassification of Class B units to common units (in units)	4,520,431
Restricted common units awards issued (in units)	0	0	0
Forfeiture of restricted common unit awards (in units)	0	0	0
Acquisition and cancellation of treasury units in connection with the vesting of equity-based awards (in units)	(630,927)	(408,241)	(255,276)
Other (in units)			(1,802)
Ending Balance (in units)	932,074,401	894,919,851	877,752,202
Restricted Common Units [Member]
Summary of changes in outstanding units [Roll Forward]
Beginning Balance (in units)	3,893,486	3,868,216	3,561,614
Common units issued in connection with underwritten offerings (in units)	0	0	0
Common units issued in connection with at-the-market program (in units)	0	0
Common units issued in connection with Duncan Merger (in units)			0
Common units issued in connection with DRIP and EUPP (in units)	0	0	0
Common units issued in connection with the vesting of unit options (in units)	0	0
Common units issued in connection with the vesting of restricted common unit awards (in units)	(1,885,348)	(1,316,603)	(924,108)
Common units issued in connection with the vesting of other types of equity-based awards (in units)		0
Conversion and reclassification of Class B units to common units (in units)	0
Restricted common units awards issued (in units)	1,774,526	1,588,738	1,414,630
Forfeiture of restricted common unit awards (in units)	(172,057)	(246,865)	(183,920)
Acquisition and cancellation of treasury units in connection with the vesting of equity-based awards (in units)	0	0	0
Other (in units)			0
Ending Balance (in units)	3,610,607	3,893,486	3,868,216
Common units [Member]
Summary of changes in outstanding units [Roll Forward]
Beginning Balance (in units)	898,813,337	881,620,418	843,681,572
Common units issued in connection with underwritten offerings (in units)	18,400,000	9,200,000	10,350,000
Common units issued in connection with at-the-market program (in units)	7,624,689	3,978,545
Common units issued in connection with Duncan Merger (in units)			24,277,310
Common units issued in connection with DRIP and EUPP (in units)	5,154,127	2,814,660	2,337,904
Common units issued in connection with the vesting of unit options (in units)	200,882	213,914
Common units issued in connection with the vesting of restricted common unit awards (in units)	0	0	0
Common units issued in connection with the vesting of other types of equity-based awards (in units)		52,168
Conversion and reclassification of Class B units to common units (in units)	4,520,431
Restricted common units awards issued (in units)	1,774,526	1,588,738	1,414,630
Forfeiture of restricted common unit awards (in units)	(172,057)	(246,865)	(183,920)
Acquisition and cancellation of treasury units in connection with the vesting of equity-based awards (in units)	(630,927)	(408,241)	(255,276)
Other (in units)			(1,802)
Ending Balance (in units)	935,685,008	898,813,337	881,620,418