Environmental Matters - Accrued Liabilities and Regulatory Assets (Detail) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Accrued Liabilities:
Accrued Liabilities	$ 751	$ 764
Regulatory assets	8,721	9,304
Manufactured gas plant sites
Accrued Liabilities:
Accrued Liabilities	671	684
Other Superfund Sites
Accrued Liabilities:
Accrued Liabilities	80	80
Superfund Sites
Accrued Liabilities:
Accrued Liabilities	751	764
Regulatory assets	897	925
CECONY
Accrued Liabilities:
Accrued Liabilities	656	666
Regulatory assets	8,071	8,613
CECONY | Manufactured gas plant sites
Accrued Liabilities:
Accrued Liabilities	576	587
CECONY | Other Superfund Sites
Accrued Liabilities:
Accrued Liabilities	80	79
CECONY | Superfund Sites
Accrued Liabilities:
Accrued Liabilities	656	666
Regulatory assets	$ 796	$ 820