Income Tax (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Income Taxes Disclosure [Line Items]
Income tax expense	$ 102,000,000	$ 124,000,000	$ 330,000,000	$ 288,000,000
Effective tax rate	37.00%	35.00%	37.00%	35.00%
Deferred tax asset, net operating loss	$ 18,000,000		$ 18,000,000
Valuation allowance	0		0
Estimated liability for uncertain tax positions	40,000,000		40,000,000
Effective income tax rate reconciliation, uncertainty of taxes			33,000,000
Effective income tax rate reconciliation, uncertainty net of federal taxes			23,000,000
Unrecognized tax benefits that would have an impact on effective tax rate	19,000,000		19,000,000
Unrecognized tax benefits that would have an impact on effective tax rate, net of taxes	13,000,000		13,000,000
Total amount of unrecognized tax benefits, if recognized, that would reduce effective tax rate	23,000,000		23,000,000
Total amount of unrecognized tax benefits, if recognized, that would reduce effective tax rate, net of federal taxes	16,000,000		16,000,000
Penalties for uncertain tax positions	0		0
CECONY
Income Taxes Disclosure [Line Items]
Income tax expense	$ 91,000,000	$ 84,000,000	$ 309,000,000	$ 264,000,000
Effective tax rate	39.00%	34.00%	39.00%	36.00%
Estimated liability for uncertain tax positions	$ 21,000,000		$ 21,000,000
Effective income tax rate reconciliation, uncertainty of taxes			17,000,000
Effective income tax rate reconciliation, uncertainty net of federal taxes			12,000,000
Unrecognized tax benefits that would have an impact on effective tax rate	$ 2,000,000		$ 2,000,000