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Commitments and Contingencies, Fuel Contracts (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Fuel Contracts [Abstract]      
Minimum payments related to SPS' extension of non-lease PPA $ 1,000    
Minimum annual payments related to SPS' extension of non-lease PPA 65    
Maximum annual payments related to SPS' extension of non-lease PPA 80    
Energy Payments      
Fuel Contracts [Abstract]      
2025 [1] 40    
2026 [1] 38    
2027 [1] 0    
2028 [1] 0    
2029 [1] 0    
Thereafter [1] 0    
Total [1] 78    
Utilities Operating Expense, Purchased Power under Long-term Contracts 25    
Capacity      
Fuel Contracts [Abstract]      
2025 16    
2026 16    
2027 0    
2028 0    
2029 0    
Thereafter 0    
Total 32    
Utilities Operating Expense, Purchased Power under Long-term Contracts 14 $ 12 $ 12
Coal      
Fuel Contracts [Abstract]      
2025 75    
2026 43    
2027 30    
2028 1    
2029 0    
Thereafter 0    
Total 149    
Natural Gas Supply [Member]      
Fuel Contracts [Abstract]      
2025 57    
2026 0    
2027 0    
2028 0    
2029 0    
Thereafter 0    
Total 57    
Natural Gas Storage and Transportation [Member]      
Fuel Contracts [Abstract]      
2025 58    
2026 58    
2027 58    
2028 52    
2029 36    
Thereafter 8    
Total $ 270    
[1] Excludes contingent energy payments for renewable energy PPAs.