Investments and Restricted Cash and Cash Equivalents and Investments - EEGH - Reconciliation (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Condensed Cash Flow Statements, Captions [Line Items]
Cash and cash equivalents	$ 1,276	$ 1,290
Restricted cash and cash equivalents	117	140
Total cash and cash equivalents and restricted cash and cash equivalents	1,406	1,445	$ 2,304	$ 1,268
Investments	5,513	6,600
Eastern Energy Gas Holdings, LLC [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Cash and cash equivalents	106	35
Restricted cash and cash equivalents	9	13
Total cash and cash equivalents and restricted cash and cash equivalents	115	48	$ 58	$ 39
Investments	$ 262	$ 244