Environmental Matters - Accrued Liabilities and Regulatory Assets (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Accrued Liabilities:
Regulatory assets	$ 7,230	$ 9,779
Manufactured Gas Plant Sites [Member]
Accrued Liabilities:
Accrued Liabilities	665	462
Other Superfund Sites [Member]
Accrued Liabilities:
Accrued Liabilities	84	83
Superfund Sites [Member]
Accrued Liabilities:
Accrued Liabilities	749	545
Regulatory assets	938	730
CECONY [Member]
Accrued Liabilities:
Regulatory assets	6,665	9,032
CECONY [Member] | Manufactured Gas Plant Sites [Member]
Accrued Liabilities:
Accrued Liabilities	562	351
CECONY [Member] | Other Superfund Sites [Member]
Accrued Liabilities:
Accrued Liabilities	82	82
CECONY [Member] | Superfund Sites [Member]
Accrued Liabilities:
Accrued Liabilities	644	433
Regulatory assets	$ 830	$ 615