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Commitments, Guarantees and Contingencies - Narrative (Details) T in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2021 USD ($) phase T	Dec. 31, 2020 USD ($)	Jun. 30, 2020 USD ($)	Mar. 08, 2021 director	Mar. 07, 2021 director	Feb. 20, 2018 USD ($)
Guarantor Obligations [Line Items]
Outstanding guarantees and other assurances aggregated	$ 1,700,000,000
Company posted collateral related to net liability positions	$ 26,000,000
Collateral posted due to credit rating downgrade		$ 25,000,000
Goal to reduce in GHG emissions	30.00%
Amount of code of conduct payment			$ 4,000,000
Number of Board Members \| director				12	11
Regulation of Waste Disposal
Guarantor Obligations [Line Items]
Accrual for environmental loss contingencies	$ 102,000,000
Environmental liabilities former gas facilities	$ 67,000,000
National Ambient Air Quality Standards
Guarantor Obligations [Line Items]
Capping of SO2 Emissions Under CSAPR \| T	2.4
Capping of NOx emissions under CSAPR \| T	1.2
National Ambient Air Quality Standards \| CSAPR
Guarantor Obligations [Line Items]
Number of phases under the EPA’s CAIR for reductions of Sulfur Dioxide and Mono-Nitrogen Oxides \| phase	2
Global Holding \| Senior Secured Term Loan \| Senior Loans \| Signal Peak, Global Rail and Affiliates
Guarantor Obligations [Line Items]
Investment ownership percentage	69.99%
FEV \| Senior Secured Term Loan \| Senior Loans \| Signal Peak \| Global Holding
Guarantor Obligations [Line Items]
Investment ownership percentage	33.33%
WMB Marketing Ventures, LLC \| Senior Secured Term Loan \| Senior Loans \| Signal Peak \| Global Holding
Guarantor Obligations [Line Items]
Investment ownership percentage	33.33333%
FE
Guarantor Obligations [Line Items]
Outstanding guarantees and other assurances aggregated	$ 1,100,000,000
Other Guarantee
Guarantor Obligations [Line Items]
Outstanding guarantees and other assurances aggregated	108,000,000
Other Assurances
Guarantor Obligations [Line Items]
Outstanding guarantees and other assurances aggregated	474,000,000
Term Loan Facility due November 2024 \| Line of Credit \| Global Holding
Guarantor Obligations [Line Items]
Face amount of debt	$ 120,000,000
EPA \| Clean Water Act
Guarantor Obligations [Line Items]
Proposed penalty amount						$ 610,000