Environmental Matters - Accrued Liabilities and Regulatory Assets (Detail) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Accrued Liabilities:
Accrued Liabilities	$ 758	$ 765
Regulatory assets	7,764	8,228
Manufactured gas plant sites
Accrued Liabilities:
Accrued Liabilities	670	679
Other Superfund Sites
Accrued Liabilities:
Accrued Liabilities	88	86
Superfund Sites
Accrued Liabilities:
Accrued Liabilities	758	765
Regulatory assets	837	904
CECONY
Accrued Liabilities:
Accrued Liabilities	664	665
Regulatory assets	7,186	7,603
CECONY | Manufactured gas plant sites
Accrued Liabilities:
Accrued Liabilities	576	579
CECONY | Other Superfund Sites
Accrued Liabilities:
Accrued Liabilities	88	86
CECONY | Superfund Sites
Accrued Liabilities:
Accrued Liabilities	664	665
Regulatory assets	$ 732	$ 800