Revenue from Contracts with Customers - EEGH (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Revenue from External Customer [Line Items]
Total Customer Revenue	$ 4,712	$ 3,516
Operating revenue	6,081	4,527
Eastern Energy Gas Holdings, LLC [Member]
Revenue from External Customer [Line Items]
Total Customer Revenue	486	555
Operating revenue	486	556
Regulated Operation [Member]
Revenue from External Customer [Line Items]
Total Customer Revenue	4,094	3,213
Regulated Operation [Member] | Eastern Energy Gas Holdings, LLC [Member]
Revenue from External Customer [Line Items]
Total Customer Revenue	296	347
Unregulated Operation [Member] | Eastern Energy Gas Holdings, LLC [Member]
Revenue from External Customer [Line Items]
Total Customer Revenue	190	208
Regulated gas transportation and storage [Member] | Regulated Operation [Member]
Revenue from External Customer [Line Items]
Total Customer Revenue	498	234
Regulated gas transportation and storage [Member] | Regulated Operation [Member] | Eastern Energy Gas Holdings, LLC [Member]
Revenue from External Customer [Line Items]
Total Customer Revenue	279	344
Regulated wholesale [Member] | Regulated Operation [Member]
Revenue from External Customer [Line Items]
Total Customer Revenue	193	77
Regulated wholesale [Member] | Regulated Operation [Member] | Eastern Energy Gas Holdings, LLC [Member]
Revenue from External Customer [Line Items]
Total Customer Revenue	17	2
Regulated other [Member] | Regulated Operation [Member]
Revenue from External Customer [Line Items]
Total Customer Revenue	25	27
Regulated other [Member] | Regulated Operation [Member] | Eastern Energy Gas Holdings, LLC [Member]
Revenue from External Customer [Line Items]
Total Customer Revenue	0	1
Non-contracts with customer revenue [Member]
Revenue from External Customer [Line Items]
Operating revenue	137	118
Non-contracts with customer revenue [Member] | Eastern Energy Gas Holdings, LLC [Member]
Revenue from External Customer [Line Items]
Operating revenue	$ 0	$ 1