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Income Taxes (Details) - USD ($)
$ in Millions
3 Months Ended 9 Months Ended 12 Months Ended
Mar. 31, 2020
Sep. 30, 2021
Sep. 30, 2020
Dec. 31, 2017
Income Tax Contingency [Line Items]        
Reduction in net deferred income tax liabilities       $ 1,140
Regulatory liability, amortization period   28 years 6 months    
Income tax expense attributable to non controlling interests   $ 0    
Domestic Tax Authority        
Income Tax Contingency [Line Items]        
Income tax benefit from amortization of an excess deferred tax liability $ 14 $ 24 $ 24