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Risk Management Credit Risks (Details) - Energy Related Derivative - USD ($)
$ in Millions
Dec. 31, 2018
Dec. 31, 2017
Credit Derivatives [Line Items]    
Letters of Credit Outstanding, Amount $ 0  
Initial Margin Requirements 9  
Variation Margin Requirements 25  
Other Current Liabilities [Member] | Contract and Over the Counter    
Credit Derivatives [Line Items]    
Derivative, Collateral, Right to Reclaim Cash $ 16  
Restricted Deposit [Member] | Contract and Over the Counter    
Credit Derivatives [Line Items]    
Derivative, Collateral, Right to Reclaim Cash   $ 1