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Price Risk Management (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Derivative [Line Items]      
Derivative Liability, Fair Value, Amount Not Offset Against Collateral   $ 2  
Net gain or loss recognized in the statement of income offset by regulatory accounting $ 12 2 $ 18
Margin Deposit Assets 6    
Right to reclaim cash collateral   0  
Credit Risk Contract [Member]      
Derivative [Line Items]      
Derivative, Net Liability Position, Aggregate Fair Value 148    
Collateral Already Posted, Aggregate Fair Value 13    
Collateral Aggregate Fair Value 142    
Right to reclaim cash collateral $ 1    
Letter of Credit [Member] | Credit Risk Contract [Member]      
Derivative [Line Items]      
Collateral posted as letter of credit 12 million    
Electricity [Member]      
Derivative [Line Items]      
Derivative Liability, Fair Value, Amount Not Offset Against Collateral   1  
Natural Gas [Member]      
Derivative [Line Items]      
Derivative Liability, Fair Value, Amount Not Offset Against Collateral   $ 1