Income Tax - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	$ 21.0
Unrecognized Tax Benefits	14.0	$ 13.0	$ 6.0	$ 12.0
Effective income tax rate reconciliation, uncertainty of taxes	3.0
Unrecognized tax benefits that would have an impact on effective tax rate	14.0
Unrecognized tax benefits that would have an impact on effective tax rate, net of tax	13.0
General Business Tax Credit
Operating Loss Carryforwards [Line Items]
Tax credit carryovers	1,022.0
Tax Year 2018 Through 2013
Operating Loss Carryforwards [Line Items]
Operating loss carryback	29.0
Net tax refund	2.5
Tax Year 2013
Operating Loss Carryforwards [Line Items]
Discrete income tax benefit	4.0
State
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards, valuation allowance	18.0
State | New York State
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	1,351.0
State | New York City
Operating Loss Carryforwards [Line Items]
Valuation allowance reversed	$ 9.0
Deferred tax asset, period of realization	10 years
CECONY
Operating Loss Carryforwards [Line Items]
Unrecognized Tax Benefits	$ 3.0	$ 2.0	$ 4.0	$ 5.0
Effective income tax rate reconciliation, uncertainty of taxes	1.0
Unrecognized tax benefits that would have an impact on effective tax rate	$ 3.0