Environmental Matters - Accrued Liabilities and Regulatory Assets (Detail) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Accrued Liabilities:
Accrued Liabilities	$ 765	$ 764
Regulatory assets	8,228	9,280
Manufactured gas plant sites
Accrued Liabilities:
Accrued Liabilities	679	684
Other Superfund Sites
Accrued Liabilities:
Accrued Liabilities	86	80
Other Superfund Sites
Accrued Liabilities:
Accrued Liabilities	765	764
Regulatory assets	904	925
CECONY
Accrued Liabilities:
Accrued Liabilities	665	666
Regulatory assets	7,603	8,589
CECONY | Manufactured gas plant sites
Accrued Liabilities:
Accrued Liabilities	579	587
CECONY | Other Superfund Sites
Accrued Liabilities:
Accrued Liabilities	86	79
CECONY | Other Superfund Sites
Accrued Liabilities:
Accrued Liabilities	665	666
Regulatory assets	$ 800	$ 820