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Revenue (Details) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2019
Sep. 30, 2018
Sep. 30, 2019
Sep. 30, 2018
Renewable Energy Sales [Member]        
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]        
Revenue from contract with customer $ 213 $ 121 $ 513 $ 418
Revenues over the remaining terms of the related contacts 215   215  
Natural Gas Transportation Services [Member]        
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]        
Revenue from contract with customer 52 $ 52 155 $ 162
Revenues over the remaining terms of the related contacts $ 2,100   $ 2,100