Summary of Significant Accounting Policies Property, Plant and Equipment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 12,906.6		$ 12,365.1
Accumulated Depreciation	3,868.1		3,727.4
Property, Plant and Equipment, Net	9,038.5		8,637.7
Public Utilities, Property, Plant and Equipment, Amount of Acquisition Adjustments, Related Accumulated Depreciation	61.8		56.3
OG&E [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	12,906.6		12,365.1
Accumulated Depreciation	3,868.1		3,727.4
Property, Plant and Equipment, Net	9,038.5		8,637.7
Capitalized Computer Software, Gross	71.3		44.3
Capitalized Computer Software, Amortization	11.0		9.6		$ 8.8
Electric Distribution [Member] | OG&E [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	4,468.6		4,229.4
Accumulated Depreciation	1,381.1		1,324.5
Property, Plant and Equipment, Net	3,087.5		2,904.9
Electric Generation Equipment [Member] | OG&E [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	4,838.6	[1]	4,657.2	[2]
Accumulated Depreciation	1,601.0	[1]	1,572.8	[2]
Property, Plant and Equipment, Net	3,237.6	[1]	3,084.4	[2]
Amount of Acquisition Adjustments	148.3		148.3
Public Utilities, Property, Plant and Equipment, Amount of Acquisition Adjustments, Related Accumulated Depreciation	61.8		56.3
Electric Transmission [Member] | OG&E [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	2,901.1	[3]	2,846.7	[4]
Accumulated Depreciation	565.5	[3]	534.2	[4]
Property, Plant and Equipment, Net	2,335.6	[3]	2,312.5	[4]
Amount of Acquisition Adjustments	3.3		3.3
Public Utilities, Property, Plant and Equipment, Amount of Acquisition Adjustments, Related Accumulated Depreciation	0.8		0.7
Finite-Lived Intangible Assets, Major Class Name [Domain] | OG&E [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	225.2		187.6
Accumulated Depreciation	145.4		135.1
Property, Plant and Equipment, Net	79.8		52.5
Property, Plant and Equipment, Other Types [Member] | OG&E [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	473.1		444.2
Accumulated Depreciation	175.1		160.8
Property, Plant and Equipment, Net	$ 298.0		$ 283.4
McClain Plant [Member]
Property, Plant and Equipment [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share	77.00%	[5]	77.00%	[6]
Property, Plant and Equipment, Gross	$ 254.4	[5]	$ 227.2	[6]
Accumulated Depreciation	83.5	[5]	78.2	[6]
Property, Plant and Equipment, Net	170.9	[5]	149.0	[6]
Jointly Owned Utility Plant, Ownership Amount of Construction Work in Progress	$ 0.2		$ 0.2
Redbud Plant [Member]
Property, Plant and Equipment [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share	51.00%	[5],[7]	51.00%	[6],[8]
Property, Plant and Equipment, Gross	$ 529.9	[5],[7]	$ 493.9	[6],[8]
Accumulated Depreciation	159.0	[5],[7]	145.3	[6],[8]
Property, Plant and Equipment, Net	370.9	[5],[7]	348.6	[6],[8]
Jointly Owned Utility Plant, Ownership Amount of Construction Work in Progress	1.4		0.9
Amount of Acquisition Adjustments	$ 148.3		$ 148.3

[1] This amount includes a plant acquisition adjustment of $148.3 million and accumulated amortization of $61.8 million.

[2] This amount includes a plant acquisition adjustment of $148.3 million and accumulated amortization of $56.3 million.

[3] This amount includes a plant acquisition adjustment of $3.3 million and accumulated amortization of $0.8 million.

[4] This amount includes a plant acquisition adjustment of $3.3 million and accumulated amortization of $0.7 million.

[5] Construction work in progress was $0.2 million and $1.4 million for the McClain and Redbud Plants, respectively.

[6] Construction work in progress was $0.2 million and $0.9 million for the McClain and Redbud Plants, respectively.

[7] This amount includes a plant acquisition adjustment of $148.3 million and accumulated amortization of $61.8 million.

[8] This amount includes a plant acquisition adjustment of $148.3 million and accumulated amortization of $56.3 million.