Income Tax - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Income Taxes Disclosure [Line Items]
Income tax expense	$ 116	$ 175	$ 243	$ 330
Re-measurement of deferred tax assets due to TCJA			42
Estimated liability for uncertain tax positions	15		15
Effective income tax rate reconciliation, uncertainty of taxes			12
Total amount of unrecognized tax benefits, if recognized, that would reduce effective tax rate	15		15
Total amount of unrecognized tax benefits, if recognized, that would reduce effective tax rate, net of federal taxes	14		14
CECONY
Income Taxes Disclosure [Line Items]
Income tax expense	119	$ 125	271	$ 274
Estimated liability for uncertain tax positions	$ 4		4
Effective income tax rate reconciliation, uncertainty of taxes			$ 3