Revenue from Contract with Customer - EEGH (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenue from External Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 15,081	$ 14,837	$ 14,972
Revenues	20,952	19,844	19,787
Non-contracts with customer revenue [Member]
Revenue from External Customer [Line Items]
Revenues	475	534	601
Eastern Energy Gas Holdings, LLC [Member]
Revenue from External Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	2,087	2,165	2,002
Revenues	2,090	2,169	1,996
Eastern Energy Gas Holdings, LLC [Member] | Non-contracts with customer revenue [Member]
Revenue from External Customer [Line Items]
Revenues	3	4	(6)
Regulated Operation [Member]
Revenue from External Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	13,553	13,433	13,612
Regulated Operation [Member] | Regulated wholesale [Member]
Revenue from External Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	366	457	501
Regulated Operation [Member] | Other customer revenue [Member]
Revenue from External Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	110	2	2
Regulated Operation [Member] | Regulated retail gas [Member]
Revenue from External Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	619	686	737
Regulated Operation [Member] | Eastern Energy Gas Holdings, LLC [Member]
Revenue from External Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	1,289	1,316	1,293
Regulated Operation [Member] | Eastern Energy Gas Holdings, LLC [Member] | Regulated wholesale [Member]
Revenue from External Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	43	9	25
Regulated Operation [Member] | Eastern Energy Gas Holdings, LLC [Member] | Other customer revenue [Member]
Revenue from External Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	4	7	19
Regulated Operation [Member] | Eastern Energy Gas Holdings, LLC [Member] | Regulated retail gas [Member]
Revenue from External Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	1,242	1,300	1,249
Nonregulated Operation [Member] | Eastern Energy Gas Holdings, LLC [Member]
Revenue from External Customer [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 798	$ 849	$ 709