Noncontrolling Interest Owner Distributions Made to Partners (Details) (USD $) In Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Sep. 30, 2011
Enogex Holdings [Member]
Distribution Made to Partners [Line Items]
Distributions to partners	$ 50.0	$ 39.6	$ 8.3	$ 97.9
OGE Holdings [Member]
Distribution Made to Partners [Line Items]
Distributions to partners	43.4	34.3	7.5	85.2
ArcLight Group [Member]
Distribution Made to Partners [Line Items]
Distributions to partners	$ 6.6	$ 5.3	$ 0.8	$ 12.7