Derivative Instruments and Hedging Activities - Fair Values of Companies' Commodity Derivatives (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Derivative Liabilities
Fair value of derivative liabilities	$ 113	$ 176
Impact of netting	(98)	(104)
Net derivatives liabilities	15	72
Derivatives Assets [Member]
Derivative Assets
Fair value of derivative assets	166	86
Impact of netting	(84)	(20)
Net derivatives assets	82	66
Derivatives Assets [Member] | Other Current Assets [Member]
Derivative Assets
Fair value of derivative assets	134	64
Derivatives Assets [Member] | Other Deferred Charges and Noncurrent Assets [Member]
Derivative Assets
Fair value of derivative assets	32	22
Derivatives Liabilities [Member] | Fair Value of Derivative Liabilities, Current [Member]
Derivative Liabilities
Fair value of derivative liabilities	82	122
Derivatives Liabilities [Member] | Fair Value of Derivative Liabilities, Long-term [Member]
Derivative Liabilities
Fair value of derivative liabilities	31	54
CECONY [Member]
Derivative Liabilities
Fair value of derivative liabilities	51	83
Impact of netting	(37)	(44)
Net derivatives liabilities	14	39
CECONY [Member] | Derivatives Assets [Member]
Derivative Assets
Fair value of derivative assets	41	27
Impact of netting	(16)	3
Net derivatives assets	25	30
CECONY [Member] | Derivatives Assets [Member] | Other Current Assets [Member]
Derivative Assets
Fair value of derivative assets	27	18
CECONY [Member] | Derivatives Assets [Member] | Other Deferred Charges and Noncurrent Assets [Member]
Derivative Assets
Fair value of derivative assets	14	9
CECONY [Member] | Derivatives Liabilities [Member] | Fair Value of Derivative Liabilities, Current [Member]
Derivative Liabilities
Fair value of derivative liabilities	32	58
CECONY [Member] | Derivatives Liabilities [Member] | Fair Value of Derivative Liabilities, Long-term [Member]
Derivative Liabilities
Fair value of derivative liabilities	$ 19	$ 25