Income Tax - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Income Taxes Disclosure [Line Items]
Income tax expense	$ 19	$ 38	$ 127	$ 156
Estimated liability for uncertain tax positions	8		8
Effective income tax rate reconciliation, uncertainty of taxes			3
Total amount of unrecognized tax benefits, if recognized, that would reduce effective tax rate	8		8
Total amount of unrecognized tax benefits, if recognized, that would reduce effective tax rate, net of federal taxes	7		7
CECONY
Income Taxes Disclosure [Line Items]
Income tax expense	27	$ 31	151	$ 150
Estimated liability for uncertain tax positions	$ 5		5
Effective income tax rate reconciliation, uncertainty of taxes			$ 2