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