Fair Value Measurements - EEGH - Fair Value Hierarchy (Details) - USD ($) $ in Millions		Mar. 31, 2021	Dec. 31, 2020
Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure		$ 8,897	$ 9,918
Derivative liabilities		(105)	(121)
Recurring [Member] | Eastern Energy Gas Holdings, LLC [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure		95	20
Derivative liabilities		(4)	(9)
Recurring [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure		6,449	7,562
Derivative liabilities		(3)	(6)
Recurring [Member] | Level 1 [Member] | Eastern Energy Gas Holdings, LLC [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure		83	0
Derivative liabilities		0	0
Recurring [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure		2,265	2,180
Derivative liabilities		(105)	(152)
Recurring [Member] | Level 2 [Member] | Eastern Energy Gas Holdings, LLC [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure		12	20
Derivative liabilities		(4)	(9)
Recurring [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure		201	197
Derivative liabilities		(36)	(19)
Recurring [Member] | Level 3 [Member] | Eastern Energy Gas Holdings, LLC [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure		0	0
Derivative liabilities		0	0
Money market mutual funds [Member] | Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	[1]	807	873
Money market mutual funds [Member] | Recurring [Member] | Eastern Energy Gas Holdings, LLC [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities		71
Money market mutual funds [Member] | Recurring [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	[1]	807	873
Money market mutual funds [Member] | Recurring [Member] | Level 1 [Member] | Eastern Energy Gas Holdings, LLC [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities		71
Money market mutual funds [Member] | Recurring [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	[1]	0	0
Money market mutual funds [Member] | Recurring [Member] | Level 2 [Member] | Eastern Energy Gas Holdings, LLC [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities		0
Money market mutual funds [Member] | Recurring [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities	[1]	0	0
Money market mutual funds [Member] | Recurring [Member] | Level 3 [Member] | Eastern Energy Gas Holdings, LLC [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities		0
Investment funds [Member] | Eastern Energy Gas Holdings, LLC [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities		12	0
Investment funds [Member] | Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities		256	201
Investment funds [Member] | Recurring [Member] | Eastern Energy Gas Holdings, LLC [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities		12
Investment funds [Member] | Recurring [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities		256	201
Investment funds [Member] | Recurring [Member] | Level 1 [Member] | Eastern Energy Gas Holdings, LLC [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities		12
Investment funds [Member] | Recurring [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities		0	0
Investment funds [Member] | Recurring [Member] | Level 2 [Member] | Eastern Energy Gas Holdings, LLC [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities		0
Investment funds [Member] | Recurring [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities		0	0
Investment funds [Member] | Recurring [Member] | Level 3 [Member] | Eastern Energy Gas Holdings, LLC [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity securities		0
Commodity Derivatives [Member] | Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets		209	188
Derivative liabilities		(81)	(54)
Commodity Derivatives [Member] | Recurring [Member] | Eastern Energy Gas Holdings, LLC [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities			(1)
Commodity Derivatives [Member] | Recurring [Member] | Level 1 [Member] | Eastern Energy Gas Holdings, LLC [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities			0
Commodity Derivatives [Member] | Recurring [Member] | Level 2 [Member] | Eastern Energy Gas Holdings, LLC [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities			(1)
Commodity Derivatives [Member] | Recurring [Member] | Level 3 [Member] | Eastern Energy Gas Holdings, LLC [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities			0
Foreign Currency Exchange Rate Derivatives [Member] | Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets		12	20
Derivative liabilities		(1)	(2)
Foreign Currency Exchange Rate Derivatives [Member] | Recurring [Member] | Eastern Energy Gas Holdings, LLC [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets		12	20
Derivative liabilities		(1)	(2)
Foreign Currency Exchange Rate Derivatives [Member] | Recurring [Member] | Level 1 [Member] | Eastern Energy Gas Holdings, LLC [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets		0	0
Derivative liabilities		0	0
Foreign Currency Exchange Rate Derivatives [Member] | Recurring [Member] | Level 2 [Member] | Eastern Energy Gas Holdings, LLC [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets		12	20
Derivative liabilities		(1)	(2)
Foreign Currency Exchange Rate Derivatives [Member] | Recurring [Member] | Level 3 [Member] | Eastern Energy Gas Holdings, LLC [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets		0	0
Derivative liabilities		0	0
Interest Rate Derivatives [Member] | Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets		80	62
Derivative liabilities		(23)	(65)
Interest Rate Derivatives [Member] | Recurring [Member] | Eastern Energy Gas Holdings, LLC [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities		(3)	(6)
Interest Rate Derivatives [Member] | Recurring [Member] | Level 1 [Member] | Eastern Energy Gas Holdings, LLC [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities		0	0
Interest Rate Derivatives [Member] | Recurring [Member] | Level 2 [Member] | Eastern Energy Gas Holdings, LLC [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities		(3)	(6)
Interest Rate Derivatives [Member] | Recurring [Member] | Level 3 [Member] | Eastern Energy Gas Holdings, LLC [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities		$ 0	$ 0

[1] Amounts are included in cash and cash equivalents, other current assets and other assets on the Consolidated Balance Sheets. The fair value of these money market mutual funds approximates cost.