Employee Benefit Plans - EEGH - Voluntary Retirement Program (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Benefit Obligation, Increase (Decrease) for Plan Amendment		$ 0	$ 0
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate		2.59%	3.24%	4.21%
Eastern Energy Gas Holdings, LLC [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	4.10%		3.63%
Eastern Energy Gas Holdings, LLC [Member] | Other Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Increase (Decrease) Due To Plan Amendment	$ 29
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	4.05%		3.44%
Eastern Energy Gas Holdings, LLC [Member] | Voluntary Retirement Program [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Cost of Providing Special and Contractual Termination Benefits			$ 74
Defined Benefit Plan, Cost of Providing Special and Contractual Termination Benefits, Net of Tax			58
Defined Benefit Plan, Benefit Obligation, Increase (Decrease) for Plan Amendment	$ 32
Defined Benefit Plan, Plan Assets, Increase (Decrease) Due To Plan Amendment	146
Defined Benefit Plan, Accumulated Benefit Obligation, Increase (Decrease) for Plan Amendment	$ 8
Eastern Energy Gas Holdings, LLC [Member] | Voluntary Retirement Program [Member] | Operations And Maintenance Expense [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Cost of Providing Special and Contractual Termination Benefits			41
Eastern Energy Gas Holdings, LLC [Member] | Voluntary Retirement Program [Member] | Other Nonoperating Income (Expense) [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Cost of Providing Special and Contractual Termination Benefits			1
Eastern Energy Gas Holdings, LLC [Member] | Voluntary Retirement Program [Member] | Income (Loss) from Discontinued Operations, Net of Tax [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Cost of Providing Special and Contractual Termination Benefits			$ 32