Income Tax - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Income Taxes Disclosure [Line Items]
Income tax expense	$ 55.0	$ 108.0
Income tax benefit due to ability to carryback a NOL under the CARES Act	4.0
Estimated liability for uncertain tax positions	13.0
Effective income tax rate reconciliation, uncertainty of taxes	10.0
Total amount of unrecognized tax benefits, if recognized, that would reduce effective tax rate	13.0
Total amount of unrecognized tax benefits, if recognized, that would reduce effective tax rate, net of federal taxes	12.0
CECONY
Income Taxes Disclosure [Line Items]
Income tax expense	95.0	$ 124.0
Estimated liability for uncertain tax positions	3.0
Effective income tax rate reconciliation, uncertainty of taxes	1.0
Total amount of unrecognized tax benefits, if recognized, that would reduce effective tax rate	3.0
Tax Year 2018 to 2013
Income Taxes Disclosure [Line Items]
Operating loss carryback	29.0
Net tax refund	2.5
Tax Year 2013
Income Taxes Disclosure [Line Items]
Discrete income tax benefit	$ 4.0