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Regulatory Matters - SPPC - Regulatory Assets (Details) - USD ($)
$ in Millions
Dec. 31, 2024
Dec. 31, 2023
Regulatory Assets [Line Items]    
Total regulatory assets $ 5,349 $ 5,565
Regulatory assets, current 1,136 1,398
Regulatory assets, noncurrent 4,213 4,167
SPPC    
Regulatory Assets [Line Items]    
Total regulatory assets 292 381
Regulatory assets, current 90 161
Regulatory assets, noncurrent $ 202 220
SPPC | Natural disaster protection plan    
Regulatory Assets [Line Items]    
Regulatory asset, amortization period 1 year  
Total regulatory assets $ 90 78
SPPC | Deferred energy costs    
Regulatory Assets [Line Items]    
Total regulatory assets $ 0 77
SPPC | Merger costs from 1999 merger    
Regulatory Assets [Line Items]    
Regulatory asset, amortization period 22 years  
Total regulatory assets $ 57 60
SPPC | Employee benefit plans    
Regulatory Assets [Line Items]    
Regulatory asset, amortization period 7 years  
Total regulatory assets $ 45 48
SPPC | Deferred operating costs    
Regulatory Assets [Line Items]    
Regulatory asset, amortization period 4 years  
Total regulatory assets $ 16 25
SPPC | Other    
Regulatory Assets [Line Items]    
Total regulatory assets $ 84 $ 93