Pension Benefits - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2014
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Estimated future employer contributions	$ 564
Pension Plan [Member] | CECONY [Member]
Defined Benefit Plan Disclosure [Line Items]
Estimated future employer contributions	524
Non-qualified Supplemental Plan [Member] | CECONY [Member]
Defined Benefit Plan Disclosure [Line Items]
Contributions	$ 13