Summary of Significant Accounting Policies Property, Plant and Equipment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	$ 12,371.2		$ 11,908.7
Accumulated Depreciation	3,727.4		3,568.8
Net property, plant and equipment	8,643.8		8,339.9
Public Utilities, Property, Plant and Equipment, Amount of Acquisition Adjustments, Related Accumulated Depreciation	56.3		50.8
Capitalized Computer Software, Amortization	$ 9.6		$ 9.0		$ 9.4
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	$ 227.2	[1]	$ 226.8	[2]
Accumulated Depreciation	78.2	[1]	71.4	[2]
Net property, plant and equipment	149.0	[1]	155.4	[2]
Jointly Owned Utility Plant, Ownership Amount of Construction Work in Progress	$ 0.2		$ 0.4
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	$ 493.9	[1],[3]	$ 496.6	[2],[4]
Accumulated Depreciation	145.3	[1],[3]	136.0	[2],[4]
Net property, plant and equipment	348.6	[1],[3]	360.6	[2],[4]
Jointly Owned Utility Plant, Ownership Amount of Construction Work in Progress	0.9		7.8
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		0.2		1.4
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	44.3		37.5
Capitalized Computer Software, Amortization	9.6		8.8		$ 8.0
OG&E [Member] | Total Property Plant and Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	12,365.1		11,902.6
Accumulated Depreciation	3,727.4		3,568.8
Net property, plant and equipment	8,637.7		8,333.8
OG&E [Member] | Electric Transmission and Distribution [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	4,229.4		4,057.1
Accumulated Depreciation	1,324.5		1,259.1
Net property, plant and equipment	2,904.9		2,798.0
OG&E [Member] | Electric Generation Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	4,657.2	[5]	4,475.0	[6]
Accumulated Depreciation	1,572.8	[5]	1,493.5	[6]
Net property, plant and equipment	3,084.4	[5]	2,981.5	[6]
Amount of Acquisition Adjustments	148.3		148.3
Public Utilities, Property, Plant and Equipment, Amount of Acquisition Adjustments, Related Accumulated Depreciation	56.3		50.8
OG&E [Member] | Electric Transmission [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	2,846.7	[7]	2,767.7	[8]
Accumulated Depreciation	534.2	[7]	506.5	[8]
Net property, plant and equipment	2,312.5	[7]	2,261.2	[8]
Amount of Acquisition Adjustments	3.3		3.3
Public Utilities, Property, Plant and Equipment, Amount of Acquisition Adjustments, Related Accumulated Depreciation	0.7		0.6
OG&E [Member] | Finite-Lived Intangible Assets, Major Class Name [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	187.6		181.8
Accumulated Depreciation	135.1		135.8
Net property, plant and equipment	52.5		46.0
OG&E [Member] | Property, Plant and Equipment, Other Types [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Gross	444.2		421.0
Accumulated Depreciation	160.8		173.9
Net property, plant and equipment	$ 283.4		$ 247.1

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

[2] Construction work in progress was $0.4 million and $7.8 million for the McClain and Redbud Plants, respectively.

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

[4] This amount includes a plant acquisition adjustment of $148.3 million and accumulated amortization of $50.8 million.

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

[6] This amount includes a plant acquisition adjustment of $148.3 million and accumulated amortization of $50.8 million.

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

[8] This amount includes a plant acquisition adjustment of $3.3 million and accumulated amortization of $0.6 million.