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	$ 12,912.7		$ 12,371.2
Accumulated Depreciation	3,868.1		3,727.4
Net property, plant and equipment	9,044.6		8,643.8
Public Utilities, Property, Plant and Equipment, Amount of Acquisition Adjustments, Related Accumulated Depreciation	61.8		56.3
Capitalized Computer Software, Amortization	$ 11.0		$ 9.6		$ 9.0
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	$ 254.4	[1]	$ 227.2	[2]
Accumulated Depreciation	83.5	[1]	78.2	[2]
Net property, plant and equipment	170.9	[1]	149.0	[2]
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%	[1],[3]	51.00%	[2],[4]
Property, Plant and Equipment, Gross	$ 529.9	[1],[3]	$ 493.9	[2],[4]
Accumulated Depreciation	159.0	[1],[3]	145.3	[2],[4]
Net property, plant and equipment	370.9	[1],[3]	348.6	[2],[4]
Jointly Owned Utility Plant, Ownership Amount of Construction Work in Progress	1.4		0.9
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
Capitalized Computer Software, Amortization	0.0		0.0		0.2
OGE Energy [Member] | Total Property Plant and Equipment [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]
Capitalized Computer Software, Gross	71.3		44.3
Capitalized Computer Software, Amortization	11.0		9.6		$ 8.8
OG&E [Member] | Total Property Plant and Equipment [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
Net property, plant and equipment	9,038.5		8,637.7
OG&E [Member] | Electric Transmission and Distribution [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
Net property, plant and equipment	3,087.5		2,904.9
OG&E [Member] | Electric Generation Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	4,838.6	[5]	4,657.2	[6]
Accumulated Depreciation	1,601.0	[5]	1,572.8	[6]
Net property, plant and equipment	3,237.6	[5]	3,084.4	[6]
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
OG&E [Member] | Electric Transmission [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	2,901.1	[7]	2,846.7	[8]
Accumulated Depreciation	565.5	[7]	534.2	[8]
Net property, plant and equipment	2,335.6	[7]	2,312.5	[8]
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
OG&E [Member] | Finite-Lived Intangible Assets, Major Class Name [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	225.2		187.6
Accumulated Depreciation	145.4		135.1
Net property, plant and equipment	79.8		52.5
OG&E [Member] | Property, Plant and Equipment, Other Types [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	473.1		444.2
Accumulated Depreciation	175.1		160.8
Net property, plant and equipment	$ 298.0		$ 283.4

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

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

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

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

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

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

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

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