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Fair Value of Financial Instruments Financial Assets and Liabilities Recognized at Fair Value (Details) - USD ($)
$ in Millions
Sep. 30, 2025
Dec. 31, 2024
Assets:    
Cash equivalents $ 112 $ 12
Debt securities:    
Domestic government 25 16
Corporate credit 10 7
Money market funds measured at NAV (2) 9 7
Non-qualified benefit plan trust: (2)    
Alternative Investment 6 4
Debt securities—domestic government 1 2
Assets from price risk management activities: (1) (3)    
Electricity 14 19
Natural gas 6 15
Total 16 11
Assets, Fair Value Disclosure 184 82
Liabilities from price risk management activities: (1) (3)    
Electricity 41 56
Natural gas 135 163
Total 176 219
Fair Value, Inputs, Level 1 [Member]    
Assets:    
Cash equivalents 112 12
Debt securities:    
Domestic government 13 10
Corporate credit 0 0
Non-qualified benefit plan trust: (2)    
Debt securities—domestic government 1 2
Assets from price risk management activities: (1) (3)    
Electricity 0 0
Natural gas 0 0
Total 126 24
Liabilities from price risk management activities: (1) (3)    
Electricity 0 0
Natural gas 0 0
Total 0 0
Fair Value, Inputs, Level 2 [Member]    
Assets:    
Cash equivalents 0 0
Debt securities:    
Domestic government 12 6
Corporate credit 10 7
Non-qualified benefit plan trust: (2)    
Debt securities—domestic government 0 0
Assets from price risk management activities: (1) (3)    
Electricity 14 18
Natural gas 5 15
Total 41 46
Liabilities from price risk management activities: (1) (3)    
Electricity 11 25
Natural gas 129 159
Total 140 184
Fair Value, Inputs, Level 3 [Member]    
Assets:    
Cash equivalents 0 0
Debt securities:    
Domestic government 0 0
Corporate credit 0 0
Non-qualified benefit plan trust: (2)    
Debt securities—domestic government 0 0
Assets from price risk management activities: (1) (3)    
Electricity 0 1
Natural gas 1 0
Total 1 1
Liabilities from price risk management activities: (1) (3)    
Electricity 30 31
Natural gas 6 4
Total $ 36 $ 35