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Revenue (Details)
$ in Millions
3 Months Ended
Mar. 31, 2018
USD ($)
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]  
Revenues over the remaining terms of the related contacts $ 2,000
Renewable Energy Sales [Member]  
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]  
Revenue from contract with customer 12
Natural Gas Transportation Services [Member]  
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]  
Revenue from contract with customer 55
Customer Contracts [Member]  
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]  
Accounts receivable balances related to contracts with customers $ 23