Derivative Instruments And Hedging Activities - Fair Values Of Companies' Commodity Derivatives (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Con Edison [Member] | Derivatives Assets [Member]
Derivatives And Hedging Activities [Line Items]
Current Other current assets	$ 110	$ 165
Impact of netting	(59)	(95)
Net derivative assets	51	70
Con Edison [Member] | Derivatives Assets [Member] | Other Current Assets [Member]
Derivatives And Hedging Activities [Line Items]
Current Other current assets	91	139
Con Edison [Member] | Derivatives Assets [Member] | Other Deferred Charges And Non-Current Assets [Member]
Derivatives And Hedging Activities [Line Items]
Current Other current assets	19	26
Con Edison [Member] | Derivatives Liabilities [Member]
Derivatives And Hedging Activities [Line Items]
Current Fair value of derivative liabilities	202	414
Impact of netting	(118)	(205)
Net derivative liabilities	84	209
Con Edison [Member] | Derivatives Liabilities [Member] | Fair Value Of Derivative Liabilities, Current [Member]
Derivatives And Hedging Activities [Line Items]
Current Fair value of derivative liabilities	149	331
Con Edison [Member] | Derivatives Liabilities [Member] | Fair Value Of Derivative Liabilities, Long-Term [Member]
Derivatives And Hedging Activities [Line Items]
Current Fair value of derivative liabilities	53	83
CECONY [Member] | Derivatives Assets [Member]
Derivatives And Hedging Activities [Line Items]
Current Other current assets	40	30
Impact of netting	(13)	(6)
Net derivative assets	27	24
CECONY [Member] | Derivatives Assets [Member] | Other Current Assets [Member]
Derivatives And Hedging Activities [Line Items]
Current Other current assets	30	16
CECONY [Member] | Derivatives Assets [Member] | Other Deferred Charges And Non-Current Assets [Member]
Derivatives And Hedging Activities [Line Items]
Current Other current assets	10	14
CECONY [Member] | Derivatives Liabilities [Member]
Derivatives And Hedging Activities [Line Items]
Current Fair value of derivative liabilities	88	175
Impact of netting	(46)	(53)
Net derivative liabilities	42	122
CECONY [Member] | Derivatives Liabilities [Member] | Fair Value Of Derivative Liabilities, Current [Member]
Derivatives And Hedging Activities [Line Items]
Current Fair value of derivative liabilities	60	127
CECONY [Member] | Derivatives Liabilities [Member] | Fair Value Of Derivative Liabilities, Long-Term [Member]
Derivatives And Hedging Activities [Line Items]
Current Fair value of derivative liabilities	$ 28	$ 48