Summary of Significant Accounting Policies Property, Plant and Equipment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020		Dec. 31, 2019		Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 13,442.2		$ 12,912.7
Accumulated Depreciation	4,067.6		3,868.1
Net property, plant and equipment	9,374.6		9,044.6
Public Utilities, Property, Plant and Equipment, Amount of Acquisition Adjustments, Related Accumulated Depreciation	$ 67.3		$ 61.8
McClain Plant [Member]
Property, Plant and Equipment [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share	77.00%	[1]	77.00%	[2]
Property, Plant and Equipment, Gross	$ 257.1	[1]	$ 254.4	[2]
Accumulated Depreciation	96.0	[1]	83.5	[2]
Net property, plant and equipment	161.1	[1]	170.9	[2]
Jointly Owned Utility Plant, Ownership Amount of Construction Work in Progress	$ 0.1		$ 0.2
Redbud Plant [Member]
Property, Plant and Equipment [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share	51.00%	[1],[3]	51.00%	[2],[4]
Property, Plant and Equipment, Gross	$ 531.8	[1],[3]	$ 529.9	[2],[4]
Accumulated Depreciation	181.9	[1],[3]	159.0	[2],[4]
Net property, plant and equipment	349.9	[1],[3]	370.9	[2],[4]
Jointly Owned Utility Plant, Ownership Amount of Construction Work in Progress	1.8		1.4
Amount of Acquisition Adjustments	148.3		148.3
OGE Energy [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	6.1		6.1
Accumulated Depreciation	0.0		0.0
Net property, plant and equipment	6.1		6.1
OG&E [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	13,436.1		12,906.6
Accumulated Depreciation	4,067.6		3,868.1
Net property, plant and equipment	9,368.5		9,038.5
Capitalized Computer Software, Gross	89.7		71.3
Capitalized Computer Software, Amortization	14.9		11.0		$ 9.6
OG&E [Member] | Total Property Plant and Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	13,436.1		12,906.6
Accumulated Depreciation	4,067.6		3,868.1
Net property, plant and equipment	9,368.5		9,038.5
OG&E [Member] | Electric Transmission and Distribution [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	4,809.9		4,468.6
Accumulated Depreciation	1,422.1		1,381.1
Net property, plant and equipment	3,387.8		3,087.5
OG&E [Member] | Electric Generation Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	4,932.2	[5]	4,838.6	[6]
Accumulated Depreciation	1,713.6	[5]	1,601.0	[6]
Net property, plant and equipment	3,218.6	[5]	3,237.6	[6]
Amount of Acquisition Adjustments	148.3		148.3
Public Utilities, Property, Plant and Equipment, Amount of Acquisition Adjustments, Related Accumulated Depreciation	67.3		61.8
OG&E [Member] | Electric Transmission [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	2,944.6	[7]	2,901.1	[8]
Accumulated Depreciation	591.7	[7]	565.5	[8]
Net property, plant and equipment	2,352.9	[7]	2,335.6	[8]
Amount of Acquisition Adjustments	3.3		3.3
Public Utilities, Property, Plant and Equipment, Amount of Acquisition Adjustments, Related Accumulated Depreciation	0.9		0.8
OG&E [Member] | Finite-Lived Intangible Assets, Major Class Name [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	254.1		225.2
Accumulated Depreciation	153.9		145.4
Net property, plant and equipment	100.2		79.8
OG&E [Member] | Property, Plant and Equipment, Other Types [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	495.3		473.1
Accumulated Depreciation	186.3		175.1
Net property, plant and equipment	$ 309.0		$ 298.0

[1] Construction work in progress was $0.1 million and $1.8 million for the McClain and Redbud Plants, respectively.

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

[3] This amount includes a plant acquisition adjustment of $148.3 million and accumulated amortization of $67.3 million.

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

[5] This amount includes a plant acquisition adjustment of $148.3 million and accumulated amortization of $67.3 million.

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

[7] This amount includes a plant acquisition adjustment of $3.3 million and accumulated amortization of $0.9 million.

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