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Long-Term Debt (Details)
$ in Millions
3 Months Ended
Mar. 31, 2021
USD ($)
Debt Instrument [Line Items]  
Percent of Principal Amount Subject to Optional Tender 100.00%
Debt Instrument, Face Amount $ 1,000.0
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 0.23%
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 0.20%
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 0.20%
Maximum [Member] | Redeemable during the next 12 months | Garfield Industrial Authority Bond [Member]  
Debt Instrument [Line Items]  
Debt Instrument, Interest Rate, Stated Percentage 0.33%
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 0.27%
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 0.27%