Income Taxes - EEGH - Net Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Beginning balance	$ 145	$ 185
Additions based on tax positions related to the current year	5	3
Additions for tax positions of prior years	6	13
Reductions for tax positions of prior years	(1)	(37)
Ending balance	153	145
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	141	139
Eastern Energy Gas Holdings, LLC [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Beginning balance	2	2
Additions for tax positions of prior years	5	0
Reductions for tax positions of prior years	(7)	0
Ending balance	0	$ 2
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	$ 2