Revenue from Contracts with Customers - EEGH - Remaining Performance Obligation (Details) $ in Millions	Mar. 31, 2021 USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Performance obligations expected to be satisfied	$ 23,952
Eastern Energy Gas Holdings, LLC [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Performance obligations expected to be satisfied	17,679
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-04-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Performance obligations expected to be satisfied	$ 3,034
Performance obligations expected to be satisfied, expected timing of satisfaction, period	12 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-04-01 | Eastern Energy Gas Holdings, LLC [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Performance obligations expected to be satisfied	$ 1,564
Performance obligations expected to be satisfied, expected timing of satisfaction, period	12 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-04-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Performance obligations expected to be satisfied	$ 20,918
Performance obligations expected to be satisfied, expected timing of satisfaction, period
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-04-01 | Eastern Energy Gas Holdings, LLC [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Performance obligations expected to be satisfied	$ 16,115
Performance obligations expected to be satisfied, expected timing of satisfaction, period