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Summary of Significant Accounting Policies Property, Plant and Equipment (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Property, Plant and Equipment [Line Items]      
Property, Plant and Equipment, Gross $ 11,185.1 $ 10,596.8  
Accumulated Depreciation 3,488.9 3,274.4  
Net property, plant and equipment 7,696.2 7,322.4  
Capitalized Computer Software, Gross 37.5 36.7  
Capitalized Computer Software, Amortization $ 9.4 $ 8.9 $ 9.5
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 $ 234.2 [1] $ 220.4 [2]  
Accumulated Depreciation 72.3 [1] 62.8 [2]  
Net property, plant and equipment 161.9 [1] 157.6 [2]  
Jointly Owned Utility Plant, Ownership Amount of Construction Work in Progress $ 0.2 $ 1.6  
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 $ 489.0 [1],[3] $ 487.5 [2],[4]  
Accumulated Depreciation 121.0 [1],[3] 101.2 [2],[4]  
Net property, plant and equipment 368.0 [1],[3] 386.3 [2],[4]  
Jointly Owned Utility Plant, Ownership Amount of Construction Work in Progress 1.8 1.3  
Amount of Acquisition Adjustments 148.3 148.3  
Public Utilities, Property, Plant and Equipment, Amount of Acquisition Adjustments, Related Accumulated Depreciation 45.3 39.8  
OGE Energy [Member]      
Property, Plant and Equipment [Line Items]      
Property, Plant and Equipment, Gross 117.7 139.0  
Accumulated Depreciation 103.3 112.7  
Net property, plant and equipment 14.4 26.3  
Capitalized Computer Software, Gross 1.0 2.4  
Capitalized Computer Software, Amortization 1.4 2.0 4.3
OGE Energy [Member] | Total Property Plant and Equipment [Member]      
Property, Plant and Equipment [Line Items]      
Property, Plant and Equipment, Gross 117.7 139.0  
Accumulated Depreciation 103.3 112.7  
Net property, plant and equipment 14.4 26.3  
OG&E [Member]      
Property, Plant and Equipment [Line Items]      
Capitalized Computer Software, Gross 36.5 34.3  
Capitalized Computer Software, Amortization 8.0 6.9 $ 5.2
OG&E [Member] | Total Property Plant and Equipment [Member]      
Property, Plant and Equipment [Line Items]      
Property, Plant and Equipment, Gross 11,067.4 10,457.8  
Accumulated Depreciation 3,385.6 3,161.7  
Net property, plant and equipment 7,681.8 7,296.1  
OG&E [Member] | Electric Transmission and Distribution [Member]      
Property, Plant and Equipment [Line Items]      
Property, Plant and Equipment, Gross 3,896.2 3,728.8  
Accumulated Depreciation 1,221.5 1,152.8  
Net property, plant and equipment 2,674.7 2,576.0  
OG&E [Member] | Electric Generation Equipment [Member]      
Property, Plant and Equipment [Line Items]      
Property, Plant and Equipment, Gross 4,155.9 [5] 3,837.4 [6]  
Accumulated Depreciation 1,493.3 [5] 1,407.0 [6]  
Net property, plant and equipment 2,662.6 [5] 2,430.4 [6]  
Amount of Acquisition Adjustments 148.3 148.3  
Public Utilities, Property, Plant and Equipment, Amount of Acquisition Adjustments, Related Accumulated Depreciation 45.3 39.8  
OG&E [Member] | Electric Transmission [Member]      
Property, Plant and Equipment [Line Items]      
Property, Plant and Equipment, Gross 2,548.8 [7] 2,454.2 [8]  
Accumulated Depreciation 481.3 [7] 440.7 [8]  
Net property, plant and equipment 2,067.5 [7] 2,013.5 [8]  
Amount of Acquisition Adjustments 3.3 3.3  
Amount of Acquistion Adjustments Related Accumulated Amortization 0.6 0.5  
OG&E [Member] | Finite-Lived Intangible Assets, Major Class Name [Member]      
Property, Plant and Equipment [Line Items]      
Property, Plant and Equipment, Gross 85.0 81.0  
Accumulated Depreciation 43.9 38.0  
Net property, plant and equipment 41.1 43.0  
OG&E [Member] | Property, Plant and Equipment, Other Types [Member]      
Property, Plant and Equipment [Line Items]      
Property, Plant and Equipment, Gross 381.5 356.4  
Accumulated Depreciation 145.6 123.2  
Net property, plant and equipment $ 235.9 $ 233.2  
[1] Construction work in progress was $0.2 million and $1.8 million for the McClain and Redbud Plants, respectively.
[2] Construction work in progress was $1.6 million and $1.3 million for the McClain and Redbud Plants, respectively.
[3] This amount includes a plant acquisition adjustment of $148.3 million and accumulated amortization of $45.3 million.
[4] This amount includes a plant acquisition adjustment of $148.3 million and accumulated amortization of $39.8 million
[5] This amount includes a plant acquisition adjustment of $148.3 million and accumulated amortization of $45.3 million.
[6] This amount includes a plant acquisition adjustment of $148.3 million and accumulated amortization of $39.8 million.
[7] This amount includes a plant acquisition adjustment of $3.3 million and accumulated amortization of $0.6 million.
[8] This amount includes a plant acquisition adjustment of $3.3 million and accumulated amortization of $0.5 million