Income Tax - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Income Taxes Disclosure [Line Items]
Income tax expense (benefit)	$ (11.0)	$ 9.0	$ 68.0	$ 64.0
Unprotected excess deferred federal income taxes amortization period			5 years
Estimated liability for uncertain tax positions	15.0		$ 15.0
Effective income tax rate reconciliation, uncertainty of taxes			3.0
Total amount of unrecognized tax benefits, if recognized, that would reduce effective tax rate	15.0		15.0
Total amount of unrecognized tax benefits, if recognized, that would reduce effective tax rate, net of federal taxes	14.0		14.0
Subsidiaries
Income Taxes Disclosure [Line Items]
Income tax expense (benefit)	(16.0)	7.0	98.0	$ 102.0
CECONY | Subsidiaries
Income Taxes Disclosure [Line Items]
Income tax expense (benefit)	(16.0)	$ 7.0
Estimated liability for uncertain tax positions	4.0		4.0
Effective income tax rate reconciliation, uncertainty of taxes			1.0
Total amount of unrecognized tax benefits, if recognized, that would reduce effective tax rate	$ 4.0		4.0
Tax Year 2013
Income Taxes Disclosure [Line Items]
Discrete income tax benefit			4.0
Tax Year 2018 to 2013
Income Taxes Disclosure [Line Items]
Operating loss carryback			$ 29.0
Net tax refund					$ 2.5