Regulatory Matters - EEGH (Details) dekathermPerDay in Millions, $ in Millions		1 Months Ended				3 Months Ended			12 Months Ended
	Aug. 01, 2020 USD ($)	Sep. 30, 2021 USD ($)	Dec. 31, 2020 USD ($)	Jan. 31, 2020 USD ($)	Dec. 31, 2014 dekathermPerDay	Jun. 30, 2021 USD ($)	Oct. 31, 2020 USD ($)	Sep. 30, 2020 USD ($)	Dec. 31, 2018 USD ($)
EGTS | Cancellation Of Atlantic Coast Pipeline Project
Schedule Of Regulatory Assets and Liabilities [Line Items]
Asset impairment charges								$ 482
Asset impairment charges, after tax								359
EGTS | Atlantic Coast Pipeline Project, Available For Potential Modified Project
Schedule Of Regulatory Assets and Liabilities [Line Items]
Asset impairment charges								10
Asset impairment charges, after tax								7
Benefit from ARO revision								29
Benefit from ARO revision, after-tax								20
Property, plant and equipment, net		$ 40
EGTS | Atlantic Coast Pipeline Project, Available For Potential Modified Project | Asset Retirement Obligation Costs
Schedule Of Regulatory Assets and Liabilities [Line Items]
Regulatory liabilities								$ 75
EGTS | 2012 FERC Case, Disallowance Of Plant, Resolved In Q4 2018
Schedule Of Regulatory Assets and Liabilities [Line Items]
Litigation settlement expense									$ 129
Litigation settlement expense, after tax									$ 94
EGTS | FERC Case, Disallowance Of Capitalized AFUDC, Resolved In December 2020
Schedule Of Regulatory Assets and Liabilities [Line Items]
Litigation settlement expense			$ 43
Litigation settlement expense, after tax			$ 31
Litigation settlement, reduction in expense						$ 11
Litigation settlement, reduction in expense, after tax						$ 8
Federal Energy Regulatory Commission | EGTS
Schedule Of Regulatory Assets and Liabilities [Line Items]
Project capacity | dekathermPerDay					1.5
General Rate Case | Federal Energy Regulatory Commission | EGTS
Schedule Of Regulatory Assets and Liabilities [Line Items]
Proposed annual cost-of-service		$ 1,100
General Rate Case | Federal Energy Regulatory Commission | EGTS | Gas Storage
Schedule Of Regulatory Assets and Liabilities [Line Items]
Proposed annual cost-of-service, rate increase		85.00%
General Rate Case | Federal Energy Regulatory Commission | EGTS | Gas Transportation
Schedule Of Regulatory Assets and Liabilities [Line Items]
Proposed annual cost-of-service, rate increase		60.00%
General Rate Case | Federal Energy Regulatory Commission | Cove Point LNG, LP
Schedule Of Regulatory Assets and Liabilities [Line Items]
Proposed annual cost-of-service				$ 182
General Rate Case, Increase In Revenue | Federal Energy Regulatory Commission | Cove Point LNG, LP
Schedule Of Regulatory Assets and Liabilities [Line Items]
Approved rate increase (decrease) amount	$ 4
General Rate Case, Decrease In Depreciation Expense | Federal Energy Regulatory Commission | Cove Point LNG, LP
Schedule Of Regulatory Assets and Liabilities [Line Items]
Approved rate increase (decrease) amount	$ (1)
General Rate Case, Provision | Federal Energy Regulatory Commission | Cove Point LNG, LP
Schedule Of Regulatory Assets and Liabilities [Line Items]
Approved rate increase (decrease) amount							$ 7