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Long-Term Debt (Details) - USD ($)
$ in Millions
3 Months Ended 12 Months Ended
Mar. 31, 2017
Dec. 31, 2016
Debt Instrument [Line Items]    
Percent of Principal Amount Subject to Optional Tender 100.00%  
Garfield Industrial Authority Bond [Member]    
Debt Instrument [Line Items]    
Debt Instrument, Maturity Date   Jan. 01, 2025
Muskogee Industrial Authority Bond Due 2025 [Member]    
Debt Instrument [Line Items]    
Debt Instrument, Maturity Date   Jan. 01, 2025
Muskogee Industrial Authority Bond Due 2027 [Member]    
Debt Instrument [Line Items]    
Debt Instrument, Maturity Date   Jun. 01, 2027
Redeemable during the next 12 months    
Debt Instrument [Line Items]    
Long-term Debt $ 135.4  
OG&E [Member] | Redeemable during the next 12 months | Garfield Industrial Authority Bond [Member]    
Debt Instrument [Line Items]    
Long term debt 47.0  
OG&E [Member] | Redeemable during the next 12 months | Muskogee Industrial Authority Bond Due 2025 [Member]    
Debt Instrument [Line Items]    
Long term debt 32.4  
OG&E [Member] | Redeemable during the next 12 months | Muskogee Industrial Authority Bond Due 2027 [Member]    
Debt Instrument [Line Items]    
Long term debt $ 56.0  
Minimum [Member] | Redeemable during the next 12 months | Garfield Industrial Authority Bond [Member]    
Debt Instrument [Line Items]    
Debt Instrument, Interest Rate, Stated Percentage 0.65%  
Minimum [Member] | Redeemable during the next 12 months | Muskogee Industrial Authority Bond Due 2025 [Member]    
Debt Instrument [Line Items]    
Debt Instrument, Interest Rate, Stated Percentage 0.65%  
Minimum [Member] | Redeemable during the next 12 months | Muskogee Industrial Authority Bond Due 2027 [Member]    
Debt Instrument [Line Items]    
Debt Instrument, Interest Rate, Stated Percentage 0.66%  
Maximum [Member] | Redeemable during the next 12 months | Garfield Industrial Authority Bond [Member]    
Debt Instrument [Line Items]    
Debt Instrument, Interest Rate, Stated Percentage 0.95%  
Maximum [Member] | Redeemable during the next 12 months | Muskogee Industrial Authority Bond Due 2025 [Member]    
Debt Instrument [Line Items]    
Debt Instrument, Interest Rate, Stated Percentage 0.90%  
Maximum [Member] | Redeemable during the next 12 months | Muskogee Industrial Authority Bond Due 2027 [Member]    
Debt Instrument [Line Items]    
Debt Instrument, Interest Rate, Stated Percentage 0.95%  
Senior Notes [Member] | OG&E [Member]    
Debt Instrument [Line Items]    
Long term debt $ 300.0  
Senior Notes [Member] | OG&E [Member] | Series due April 1, 2047 [Member]    
Debt Instrument [Line Items]    
Debt Instrument, Interest Rate, Stated Percentage 4.15%  
Long term debt $ 300.0  
Debt Instrument, Maturity Date Apr. 01, 2047  
Senior Notes [Member] | OG&E [Member] | Series Due July 15, 2017 [Member]    
Debt Instrument [Line Items]    
Debt Instrument, Interest Rate, Stated Percentage 6.50%  
Long term debt $ 125.0  
Debt Instrument, Maturity Date Jul. 15, 2017