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Asset Retirement Obligations (Details) - USD ($)
$ in Millions
3 Months Ended 12 Months Ended
Sep. 30, 2020
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Asset Retirement Obligation, Revision of Estimate   $ 17 $ 82 $ 27
Asset Retirement Obligation, Accretion Expense   10 9 8
Asset Retirement Obligation, Liabilities Incurred   $ 3 0 0
Document Period End Date   Dec. 31, 2020    
Decommissioning Liability, Noncurrent   $ 6    
Asset Retirement Obligation, Cash Paid to Settle   18 9 $ 5
Recorded Third-Party Environmental Recoveries, Amount   5 $ 4  
Asset Retirement Obligation, Liabilities Settled   $ 4    
Asset Retirement Obligations, Significant Changes   13 million    
Utility Plant [Domain]        
Asset Retirement Obligation, Accretion Expense   $ 4    
Asset Retirement Obligation, Liabilities Incurred   5    
Asset Retirement Obligation, Period Increase (Decrease)   $ 8    
Non Utility [Member] [Member]        
Asset Retirement Obligation, Revision of Estimate $ 4      
Asset Retirement Obligation, Liabilities Incurred 3      
Asset Retirement Obligation, Period Increase (Decrease) $ 21