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Note 8 - Derivatives and Hedging (Details Textual)
$ in Millions
Dec. 31, 2024
USD ($)
Jun. 28, 2023
USD ($)
Aug. 20, 2021
USD ($)
Number of Interest Rate Derivatives Held 4    
Unsecured Term Notes Payable, at 30-day SOFR Average 1.20% Due August 20, 2026 [Member]      
Debt Instrument, Face Amount     $ 15
Roanoke Gas Company [Member]      
Number of Interest Rate Derivatives Held 2    
Roanoke Gas Company [Member] | Unsecured Debt [Member] | Unsecured Term Notes Payable, at 30-day SOFR Average 1.20% Due August 20, 2026 [Member]      
Debt Instrument, Face Amount $ 15    
Derivative, Fixed Interest Rate 2.00%    
Roanoke Gas Company [Member] | Unsecured Debt [Member] | Unsecured Term Notes Payable, at 30-day LIBOR Plus 100 Basis Points, Due October 1, 2028 [Member]      
Debt Instrument, Face Amount $ 10    
Derivative, Fixed Interest Rate 2.49%    
RGC Midstream LLC [Member] | Unsecured Debt [Member]      
Debt Instrument, Face Amount $ 8 $ 8  
Derivative, Fixed Interest Rate 2.443%    
RGC Midstream LLC [Member] | Unsecured Debt [Member] | Unsecured Term Notes Payable, at 3.58%, Due on October 2, 2027 [Member]      
Debt Instrument, Face Amount $ 8    
RGC Midstream LLC [Member] | Unsecured Term Notes [Member] | Unsecured Term Notes Payable, at 30-day LIBOR Plus 1.15% Due June 12, 2026 [Member]      
Debt Instrument, Face Amount $ 14    
Derivative, Fixed Interest Rate 3.24%