Asset Retirement Obligations (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Regulatory Liabilities [Line Items]
Accrued liability - asset retirement obligations	$ 314	$ 246
Increase in liabilities for asset retirement obligations due to changes in estimated cash flows	98
Asset retirement obligations, accretion expense	10
Asset retirement obligations, liabilities settled	40
Asset retirement obligations, reductions	36	37
CECONY
Regulatory Liabilities [Line Items]
Accrued liability - asset retirement obligations	287	227
Increase in liabilities for asset retirement obligations due to changes in estimated cash flows	91
Asset retirement obligations, accretion expense	9
Asset retirement obligations, liabilities settled	40
Asset retirement obligations, reductions	$ 36	$ 37