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Related Party Transactions - EEGH - Significant Transactions (Details) - USD ($)
$ in Millions
3 Months Ended 12 Months Ended
Mar. 31, 2021
Mar. 31, 2020
Dec. 31, 2018
Related Party Transaction [Line Items]      
Capitalized expenditures $ 1,295 $ 1,356  
Eastern Energy Gas Holdings, LLC [Member]      
Related Party Transaction [Line Items]      
Capitalized expenditures $ 55 76  
Eastern Energy Gas Holdings, LLC [Member] | Affiliated Entity [Member]      
Related Party Transaction [Line Items]      
Sales of natural gas and transportation and storage services   64  
Purchases of natural gas and transportation and storage services / Services provided to related parties   3 $ 32
Services provided by related parties [1]   43  
Capitalized expenditures   $ 3  
[1] Includes capitalized expenditures of $3 million.