Noncontrolling Interests Distributions Made to Partners (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Mar. 31, 2012	Jun. 30, 2012
OGE Holdings [Member]
Distribution Made to Partners [Line Items]
Distributions to partners	$ 10.1	$ 24.4	$ 34.5
ArcLight Group [Member]
Distribution Made to Partners [Line Items]
Distributions to partners	2.4	5.6	8.0
Enogex Holdings [Member]
Distribution Made to Partners [Line Items]
Distributions to partners	12.5	30.0	42.5
Atoka [Member]
Distribution Made to Partners [Line Items]
Distributions to partners			0
Atoka [Member]
Distribution Made to Partners [Line Items]
Contributions from noncontrolling interest partner			$ 1.0