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Commitments and Contingencies - Narrative (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Other Commitments [Line Items]      
Capacity and energy requirement costs $ 5.6 $ 13.1 $ 11.5
Coal purchase commitment costs 43.7 45.1 40.4
Land easement non-lease payments expense 1.8 $ 1.4 $ 1.3
OTP | Federal Energy Regulatory Commission      
Other Commitments [Line Items]      
Estimated liability of refund obligation 2.8    
OTP | Construction Programs      
Other Commitments [Line Items]      
Long-term purchase commitment, amount 17.1    
OTP | OTP Land Easements      
Other Commitments [Line Items]      
Long-term purchase commitment, amount $ 62.4    
Long-term purchase commitment, period 99 years