Asset Retirement Obligations - Accrued Liability for Asset Retirement Obligations and Regulatory Liabilities (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Regulatory Liabilities [Line Items]
Accrued liability - asset retirement obligations	$ 143	$ 159
Regulatory liabilities - allowance for cost of removal less salvage	1,728	1,202
Allowance for Cost Removal Less Salvage [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities - allowance for cost of removal less salvage	540	503
CECONY [Member]
Regulatory Liabilities [Line Items]
Accrued liability - asset retirement obligations	143	158
Regulatory liabilities - allowance for cost of removal less salvage	1,598	1,077
CECONY [Member] | Allowance for Cost Removal Less Salvage [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities - allowance for cost of removal less salvage	$ 453	$ 420