Summary of Significant Accounting Policies Property, Plant and Equipment (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 8,749.7		$ 8,143.2
Accumulated Depreciation	2,705.6		2,592.3
Property, Plant and Equipment, Net	6,044.1		5,550.9
McClain Plant [Member]
Property, Plant and Equipment [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share	77.00%
Property, Plant and Equipment, Gross	182.1
Accumulated Depreciation	56.3
Property, Plant and Equipment, Net	125.8
Redbud Plant [Member]
Property, Plant and Equipment [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share	51.00%
Property, Plant and Equipment, Gross	458.5	[1]
Accumulated Depreciation	69.5	[1]
Property, Plant and Equipment, Net	389.0	[1]
Amount of Acquisition Adjustments	148.3
Amount of Acquistion Adjustments Related Accumulated Amortization	23.3
OG&E [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	8,749.7		8,143.2
Accumulated Depreciation	2,705.6		2,592.3
Property, Plant and Equipment, Net	6,044.1		5,550.9
Capitalized Computer Software, Amortization	4.2		1.8		2.6
Electric Transmission and Distribution Equipment [Member] | OG&E [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	3,222.7		2,981.3
Accumulated Depreciation	969.6		920.3
Property, Plant and Equipment, Net	2,253.1		2,061.0
Electric Generation Equipment [Member] | OG&E [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	3,446.6	[2]	3,360.6	[3]
Accumulated Depreciation	1,242.4	[2]	1,215.8	[3]
Property, Plant and Equipment, Net	2,204.2	[2]	2,144.8	[3]
Amount of Acquistion Adjustments Related Accumulated Amortization			17.9
Transmission Equipment [Member] | OG&E [Member]
Property, Plant and Equipment [Line Items]
Amount of Acquisition Adjustments	3.3		3.3
Amount of Acquistion Adjustments Related Accumulated Amortization	0.3		0.2
Electric Transmission [Member] | OG&E [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	1,712.6	[4]	1,464.2	[5]
Accumulated Depreciation	359.8	[4]	339.6	[5]
Property, Plant and Equipment, Net	1,352.8	[4]	1,124.6	[5]
Finite-Lived Intangible Assets, Major Class Name [Domain] | OG&E [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	50.2		43.2
Accumulated Depreciation	25.0		20.3
Property, Plant and Equipment, Net	25.2		22.9
Property, Plant and Equipment, Other Types [Member] | OG&E [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	317.6		293.9
Accumulated Depreciation	108.8		96.3
Property, Plant and Equipment, Net	$ 208.8		$ 197.6

[1] This amount includes a plant acquisition adjustment of $148.3 million and accumulated amortization of $23.3 million.

[2] This amount includes a plant acquisition adjustment of $148.3 million and accumulated amortization of $23.3 million.

[3] This amount includes a plant acquisition adjustment of $148.3 million and accumulated amortization of $17.9 million.

[4] This amount includes a plant acquisition adjustment of $3.3 million and accumulated amortization of $0.3 million.

[5] This amount includes a plant acquisition adjustment of $3.3 million and accumulated amortization of $0.2 million.