Other Material Contingencies - Con Edison Transmission (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2021	Dec. 31, 2020
Guarantor Obligations [Line Items]
Guarantee obligations maximum exposure	$ 2,311	$ 2,042
Stagecoach Gas Services LLC
Guarantor Obligations [Line Items]
Guarantee obligations maximum exposure	$ 7
Payment Guarantee by CET Electric of Contributions to New York Transco LLC
Guarantor Obligations [Line Items]
Estimated project cost percentage	175.00%
NY Transco | Payment Guarantee by CET Electric of Contributions to New York Transco LLC
Guarantor Obligations [Line Items]
Ownership interest, percentage	45.70%