Summary of Significant Accounting Policies - EEGH - New Accounting Pronouncements (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total equity	$ 46,977	$ 32,578	$ 29,723	$ 28,308
Eastern Energy Gas Holdings, LLC [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total equity	$ 6,995	$ 10,229	$ 8,865	8,495
Eastern Energy Gas Holdings, LLC [Member] | Cumulative Effect, Period of Adoption, Adjustment [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total equity				$ 3