Summary of Significant Accounting Policies and Other Matters - Investments (Details) $ in Millions	12 Months Ended
	Dec. 31, 2021 USD ($) mi	Dec. 31, 2020 USD ($)	Dec. 30, 2021 USD ($)	Jun. 30, 2021 USD ($)	May 31, 2021 USD ($)	Mar. 31, 2021 USD ($)	Dec. 30, 2020 USD ($)	Jan. 31, 2016
Schedule of Equity Method Investments [Line Items]
Supplemental retirement income plan assets	$ 525.0	$ 465.0
Deferred income plan assets	102.0	92.0
Other	3.0	3.0
Total investments	853.0	1,816.0
Stagecoach
Schedule of Equity Method Investments [Line Items]
Loss on sale of investment (pre-tax)	212.0
Loss on sale of investment	147.0
Equity method investments				$ 630.0		$ 667.0
Mountain Valley Pipeline
Schedule of Equity Method Investments [Line Items]
Equity method investments	530.0	530.0
CET | Stagecoach
Schedule of Equity Method Investments [Line Items]
Equity method investments	0.0	845.0
CET | Mountain Valley Pipeline
Schedule of Equity Method Investments [Line Items]
Equity method investments	111.0	342.0
CET | New York Transco, LLC
Schedule of Equity Method Investments [Line Items]
Equity method investments	112.0	69.0
CET | Stagecoach | Subsidiaries
Schedule of Equity Method Investments [Line Items]
Proceeds from sale	$ 1,225.0
Equity method investment, ownership percentage	50.00%
Impairment loss	$ 414.0
CET Gas | Stagecoach | Subsidiaries
Schedule of Equity Method Investments [Line Items]
Proceeds from sale	629.0
CECONY
Schedule of Equity Method Investments [Line Items]
Supplemental retirement income plan assets	499.0	439.0
Deferred income plan assets	102.0	92.0
Other	7.0	10.0
Total investments	608.0	541.0
CECONY | CET | Stagecoach
Schedule of Equity Method Investments [Line Items]
Equity method investments	0.0	0.0
CECONY | CET | Mountain Valley Pipeline
Schedule of Equity Method Investments [Line Items]
Equity method investments	0.0	0.0
CECONY | CET | New York Transco, LLC
Schedule of Equity Method Investments [Line Items]
Equity method investments	$ 0.0	$ 0.0
CET Gas | Mountain Valley Pipeline
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage	10.20%	11.30%
Impairment loss	$ 231.0	$ 320.0
Equity method investments		530.0
Number of miles in pipeline construction | mi	300
Carrying value of investment	$ 111.0	$ 342.0	$ 342.0				$ 662.0
Expected reduction in equity interest	8.50%
Project, percent completion	92.00%	94.00%
Long -term firm transportation contract period	20 years
Cash flows discount rate	8.30%
Deferred tax assets	$ 130.0	$ 53.0
Increase in deferred tax assets	77.0
Impairment loss, after tax	$ 162.0	$ 223.0
Aggregate project cost					$ 6,200.0
CET Gas | Mountain Valley Pipeline | Mountain Valley Pipeline
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage								12.50%
CET Electric | New York Transco, LLC
Schedule of Equity Method Investments [Line Items]
Equity method investment, ownership percentage	45.70%