Income Tax (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Income Taxes Disclosure [Line Items]
Income tax expense	$ 270,000,000	$ 314,000,000	$ 599,000,000	$ 602,000,000
Effective tax rate	37.00%	39.00%	37.00%	37.00%
Deferred tax asset, net operating loss	$ 19,000,000		$ 19,000,000
Valuation allowance	0		0
Estimated liability for uncertain tax positions	41,000,000		41,000,000
Effective income tax rate reconciliation, uncertainty of taxes			35,000,000
Effective income tax rate reconciliation, uncertainty net of federal taxes			24,000,000
Unrecognized tax benefits that would have an impact on effective tax rate	21,000,000		21,000,000
Unrecognized tax benefits that would have an impact on effective tax rate, net of taxes	15,000,000		15,000,000
Total amount of unrecognized tax benefits, if recognized, that would reduce effective tax rate	25,000,000		25,000,000
Total amount of unrecognized tax benefits, if recognized, that would reduce effective tax rate, net of federal taxes	18,000,000		18,000,000
Interest expense for uncertain tax positions	0		0
Penalties for uncertain tax positions	0		0
Accrued interest on uncertain tax positions	0		0		$ 0
CECONY
Income Taxes Disclosure [Line Items]
Income tax expense	$ 242,000,000	$ 226,000,000	$ 551,000,000	$ 491,000,000
Effective tax rate	38.00%	37.00%	38.00%	36.00%
Estimated liability for uncertain tax positions	$ 21,000,000		$ 21,000,000
Effective income tax rate reconciliation, uncertainty of taxes			18,000,000
Effective income tax rate reconciliation, uncertainty net of federal taxes			13,000,000
Unrecognized tax benefits that would have an impact on effective tax rate	$ 4,000,000		$ 4,000,000