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Fair Value of FInancial Instruments Schedule of Fair Value (Details) - USD ($)
$ in Millions
Dec. 31, 2020
Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash and Cash Equivalents, Fair Value Disclosure $ 255 $ 26
Domestic government, Debt securities 20 24
Corporate debt securities held in decommissioning trust assets 13 9
Money market funds 12 13
Fair Value - Money market funds 1 1
Domestic Equity Securities 7 7
Debt securities - domestic government 1 1
Electricity 8 16
Natural gas 37 22
Financial Instruments, Owned, at Fair Value 12 13
Assets, Fair Value Disclosure 354 119
Liabilities from price risk management activities: [Abstract]    
Electricity 146 119
Natural gas 5 12
Liabilities, Fair Value Disclosure 151 131
Fair Value, Inputs, Level 1 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash and Cash Equivalents, Fair Value Disclosure 255 26
Domestic government, Debt securities 9 8
Corporate debt securities held in decommissioning trust assets 0 0
Fair Value - Money market funds 1 1
Domestic Equity Securities 7 7
Debt securities - domestic government 1 1
Electricity 0 0
Natural gas 0 0
Financial Instruments, Owned, at Fair Value 273 43
Liabilities from price risk management activities: [Abstract]    
Electricity 0 0
Natural gas 0 0
Liabilities, Fair Value Disclosure 0 0
Fair Value, Inputs, Level 2 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash and Cash Equivalents, Fair Value Disclosure 0 0
Domestic government, Debt securities 11 16
Corporate debt securities held in decommissioning trust assets 13 9
Fair Value - Money market funds 0 0
Domestic Equity Securities 0 0
Debt securities - domestic government 0 0
Electricity 4 9
Natural gas 36 21
Financial Instruments, Owned, at Fair Value 64 55
Liabilities from price risk management activities: [Abstract]    
Electricity 5 14
Natural gas 4 12
Liabilities, Fair Value Disclosure 9 26
Fair Value, Inputs, Level 3 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash and Cash Equivalents, Fair Value Disclosure 0 0
Domestic government, Debt securities 0 0
Corporate debt securities held in decommissioning trust assets 0 0
Money market funds 0  
Fair Value - Money market funds   0
Domestic Equity Securities 0 0
Debt securities - domestic government 0 0
Electricity 4 7
Natural gas 1 1
Financial Instruments, Owned, at Fair Value 5 8
Liabilities from price risk management activities: [Abstract]    
Electricity 141 105
Natural gas 1 0
Liabilities, Fair Value Disclosure 142 105
Non Qualified Benefit Plans [Member]    
Liabilities from price risk management activities: [Abstract]    
Insurance contracts, at cash surrender value $ 33 $ 29