Pension Benefits - Additional Information (Detail) $ in Millions	9 Months Ended
	Sep. 30, 2015 USD ($)
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Expected contributions	$ 750
Contributions	747
CECONY | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Expected contributions	697
Contributions	694
CECONY | Non-qualified Supplemental Plan
Defined Benefit Plan Disclosure [Line Items]
Expected contributions	$ 16