Income Tax - Additional Information (Details) - USD ($)	1 Months Ended	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Income Taxes Disclosure [Line Items]
Income tax expense		$ 38,000,000	$ 102,000,000	$ 156,000,000	$ 330,000,000
Estimated liability for uncertain tax positions		10,000,000		10,000,000
Effective income tax rate reconciliation, uncertainty of taxes				5,000,000
Effective income tax rate reconciliation, uncertainty net of federal taxes				4,000,000
Total amount of unrecognized tax benefits, if recognized, that would reduce effective tax rate		10,000,000		10,000,000
Total amount of unrecognized tax benefits, if recognized, that would reduce effective tax rate, net of federal taxes		9,000,000		9,000,000
Interest expense for uncertain tax positions		0	0	0	0
Penalties for uncertain tax positions		0	0	0	0
Accrued interest on uncertain tax positions		0		0		$ 0
Federal
Income Taxes Disclosure [Line Items]
Settlement of uncertain federal tax positions	$ 3,000,000
CECONY
Income Taxes Disclosure [Line Items]
Income tax expense		31,000,000	$ 91,000,000	150,000,000	$ 309,000,000
Estimated liability for uncertain tax positions		$ 4,000,000		4,000,000
Effective income tax rate reconciliation, uncertainty of taxes				$ 2,000,000