Income Tax - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Income Taxes Disclosure [Line Items]
Income tax expense	$ 119.0	$ 116.0	$ 183.0	$ 243.0
Income tax benefit due to ability to carryback a NOL under the CARES Act			$ 4.0
Unprotected excess deferred federal income taxes amortization period			5 years
Estimated liability for uncertain tax positions	14.0		$ 14.0
Effective income tax rate reconciliation, uncertainty of taxes			3.0
Total amount of unrecognized tax benefits, if recognized, that would reduce effective tax rate	14.0		14.0
Total amount of unrecognized tax benefits, if recognized, that would reduce effective tax rate, net of federal taxes	13.0		13.0
CECONY
Income Taxes Disclosure [Line Items]
Income tax expense	97.0	$ 119.0	199.0	$ 271.0
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 2018 to 2013
Income Taxes Disclosure [Line Items]
Operating loss carryback			29.0
Net tax refund	2.5		$ 2.5
Tax Year 2013
Income Taxes Disclosure [Line Items]
Discrete income tax benefit	$ 4.0