Environmental Matters - Accrued Liabilities and Regulatory Assets (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Accrued Liabilities:
Regulatory assets	$ 7,090	$ 7,230
Manufactured Gas Plant Sites [Member]
Accrued Liabilities:
Accrued Liabilities	663	665
Other Superfund Sites [Member]
Accrued Liabilities:
Accrued Liabilities	78	84
Superfund Sites [Member]
Accrued Liabilities:
Accrued Liabilities	741	749
Regulatory assets	921	938
CECONY [Member]
Accrued Liabilities:
Regulatory assets	6,527	6,665
CECONY [Member] | Manufactured Gas Plant Sites [Member]
Accrued Liabilities:
Accrued Liabilities	560	562
CECONY [Member] | Other Superfund Sites [Member]
Accrued Liabilities:
Accrued Liabilities	77	82
CECONY [Member] | Superfund Sites [Member]
Accrued Liabilities:
Accrued Liabilities	637	644
Regulatory assets	$ 814	$ 830