Equity-based Awards (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2011		Jun. 30, 2010		Jun. 30, 2011		Jun. 30, 2010		Dec. 31, 2010
Equity-based compensation expense [Abstract]
Total compensation expense	$ 13.2		$ 11.1		$ 25.0		$ 19.8
Restricted Common Unit Awards [Member]
Equity-based compensation expense [Abstract]
Total compensation expense	12.1		7.9		23.5		13.7
Equity-based awards, additional disclosures [Abstract]
Cash distributions paid to restricted common unit holders	2.7		2.3		4.8		3.8
Total intrinsic value of restricted common unit awards vesting during period	20.5		10.3		35.2		11.4
Unrecognized compensation cost	73.5				73.5
Restricted Common Unit Awards [Member] | Enterprise [Member]
Summary of awards activity, equity instruments other than options [Roll Forward]
Beginning of period (in units)					3,561,614
Granted (in units)					1,359,230	[1]
Vested (in units)					(828,545)
Forfeited (in units)					(75,857)
End of period (in units)	4,016,442				4,016,442
Summary of awards activity, equity instruments other than options, additional disclosures [Abstract]
Weighted-average grant date fair value per unit, at beginning of period (in dollars per unit)					$ 29.78	[2]
Granted weighted-average grant date fair value per unit (in dollars per unit)					$ 43.68	[1],[2]
Vested weighted-average grant date fair value per unit (in dollars per unit)					$ 31.57	[2]
Forfeited weighted-average grant date fair value per unit (in dollars per unit)					$ 32.67	[2]
Weighted-average grant date fair value per unit, at end of period (in dollars per unit)	$ 34.06	[2]			$ 34.06	[2]
Equity-based awards, additional disclosures [Abstract]
Aggregate grant date fair value					59.4
Minimum grant date market price of common units (in dollars per unit)					$ 40.54
Maximum grant date market price of common units (in dollars per unit)					$ 43.70
Estimated forfeiture rate (in hundredths)					4.60%
Unrecognized compensation cost	69.4				69.4
Recognition period for total unrecognized compensation cost (in years)					2.0
Restricted Common Unit Awards [Member] | Duncan Energy Partners [Member]
Summary of awards activity, equity instruments other than options [Roll Forward]
Beginning of period (in units)					0
Granted (in units)					3,666	[3]
Vested (in units)					(3,666)	[3]
End of period (in units)	0				0
Summary of awards activity, equity instruments other than options, additional disclosures [Abstract]
Weighted-average grant date fair value per unit, at beginning of period (in dollars per unit)					$ 0	[2]
Granted weighted-average grant date fair value per unit (in dollars per unit)					$ 32.56	[2],[3]
Vested weighted-average grant date fair value per unit (in dollars per unit)					$ 32.56	[2],[3]
Weighted-average grant date fair value per unit, at end of period (in dollars per unit)	$ 0	[2]			$ 0	[2]
Equity-based awards, additional disclosures [Abstract]
Aggregate grant date fair value					0.1
Grant date market price of common units (in dollars per unit)					$ 32.56
Unit Option Awards [Member]
Equity-based compensation expense [Abstract]
Total compensation expense	0.8		0.7		1.7		1.4
Summary of awards activity, options [Roll Forward]
Number of Units (in units)	3,753,420				3,753,420				3,753,420
Summary of awards activity, options, additional disclosures [Abstract]
Weighted average strike price (in dollars per unit)	$ 28.08				$ 28.08				$ 28.08
Weighted average remaining contractual term (in years)	3.1				3.1				3.6
Aggregate intrinsic value	7.3	[4]			7.3	[4]			0	[4]
Exercisable (in units)	0	[5]			0	[5]
Exercisable - Weighted average remaining contractual term (in years)	0	[5]			0	[5]
Exercisable - Aggregate intrinsic value	0	[4],[5]			0	[4],[5]
Option awards vested during period (in units)					612,280
Awards vest during the remainder of 2011 (in units)	100,000				100,000
Awards vest during 2012 (in units)	736,000				736,000
Awards vest during 2013 (in units)	1,520,140				1,520,140
Awards vest during 2014 (in units)	785,000				785,000
Equity-based awards, additional disclosures [Abstract]
Total intrinsic value of unit option awards exercised during period	0		1.3		0		2.2
Cash received from EPCO in connection with the exercise of unit option awards	0		1.0		0		1.6
Unit option-related reimbursements to EPCO	0		1.3		0		2.2
Unrecognized compensation cost	5.0				5.0
Unit Option Awards [Member] | Enterprise [Member]
Equity-based awards, additional disclosures [Abstract]
Unrecognized compensation cost	4.5				4.5
Recognition period for total unrecognized compensation cost (in years)					1.9
Other Equity-based Awards [Member]
Equity-based compensation expense [Abstract]
Total compensation expense	0.3	[6]	2.5	[6]	(0.2)	[6]	4.7	[6]
Unit Appreciation Rights [Member]
Equity-based compensation expense [Abstract]
Total compensation expense			0.2		(0.6)		0.3
Summary of awards activity, equity instruments other than options [Roll Forward]
Beginning of period (in units)					170,104
Vested (in units)					(10,939)
Settled or forfeited (in units)					(45,000)
End of period (in units)	114,165				114,165
Accrued liability for UARs	0.4				0.4				1.0
Summary of awards activity, equity instruments other than options, additional disclosures [Abstract]
Weighted-average grant date fair value per unit, at end of period (in dollars per unit)	$ 37.00				$ 37.00
Employee Partnerships [Member]
Equity-based compensation expense [Abstract]
Total compensation expense			$ 1.9				$ 3.8
Long-Term Incentive Plan (1998) [Member]
Equity-based compensation expense [Abstract]
Maximum number of common units that may be issued as awards (in units)	7,000,000				7,000,000
Remaining number of common units available to be issued as awards (in units)	1,475,190				1,475,190
Long-Term Incentive Plan (2008) [Member]
Equity-based compensation expense [Abstract]
Maximum number of common units that may be issued as awards (in units)	10,000,000				10,000,000
Remaining number of common units available to be issued as awards (in units)	4,706,877				4,706,877
Long-Term Incentive Plan (2010) [Member]
Equity-based compensation expense [Abstract]
Maximum number of common units that may be issued as awards (in units)	500,000				500,000
Remaining number of common units available to be issued as awards (in units)	489,986				489,986

[1] The aggregate grant date fair value of restricted common unit awards issued in 2011 was $59.4 million based on a grant date market price of our common units ranging from $40.54 to $43.70 per unit. An estimated annual forfeiture rate of 4.6% 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.

[3] The aggregate grant date fair value of restricted common unit awards issued in 2011 was $0.1 million based on a grant date market price of Duncan Energy Partners' common units of $32.56 per unit. These awards vested upon issuance.

[4] Aggregate intrinsic value reflects fully vested unit options at the date indicated. There were no vested unit options outstanding at December 31, 2010.

[5] We were committed to issue 3,753,420 of our common units at June 30, 2011 if all outstanding options awarded were exercised. Option awards outstanding at June 30, 2011 include 612,280 awards that vested during the first six months of 2011. Of the remaining outstanding option awards at June 30, 2011, 100,000, 736,000, 1,520,140 and 785,000 will vest in 2011, 2012, 2013, and 2014, respectively. These unit option awards become exercisable in the calendar year following the year in which they vest.

[6] Primarily consists of unit appreciation rights ("UARs"), phantom units and similar awards. Also, the amounts presented for 2010 consist of awards related to limited partnership interests in the Employee Partnerships.