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Regulatory Matters (Other Regulatory Matters) (Details) - USD ($)
1 Months Ended 3 Months Ended
Jun. 30, 2020
Mar. 31, 2021
Mar. 31, 2020
Feb. 28, 2021
Dec. 31, 2020
Public Utilities, General Disclosures [Line Items]          
Equity in losses (earnings) of unconsolidated affiliates   $ 17,000,000 $ (44,000,000)    
Current Liabilities: Other   1,858,000,000     $ 2,936,000,000
Asset retirement obligations   709,000,000     718,000,000
ACP          
Public Utilities, General Disclosures [Line Items]          
Current Liabilities: Other   46,000,000     $ 936,000,000
ACP | ACP          
Public Utilities, General Disclosures [Line Items]          
Equity in losses (earnings) of unconsolidated affiliates $ 2,100,000,000        
Current Liabilities: Other   38,000,000      
Other Noncurrent Liabilities   48,000,000      
ACP | ACP | Current liabilities          
Public Utilities, General Disclosures [Line Items]          
Guarantor obligations settled       $ 855,000,000  
Asset retirement obligations   $ 86,000,000      
ACP          
Public Utilities, General Disclosures [Line Items]          
Joint owner ownership percentage   47.00%