Fair Value Measurements - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended		12 Months Ended				12 Months Ended				12 Months Ended				12 Months Ended			12 Months Ended			12 Months Ended		12 Months Ended							12 Months Ended				12 Months Ended				12 Months Ended					12 Months Ended		12 Months Ended			12 Months Ended					12 Months Ended				12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended			12 Months Ended					12 Months Ended				12 Months Ended		12 Months Ended		12 Months Ended			12 Months Ended		12 Months Ended							12 Months Ended				12 Months Ended			12 Months Ended			12 Months Ended		12 Months Ended
	Dec. 31, 2011	Dec. 31, 2012 Con Edison [Member]	Dec. 31, 2011 CECONY [Member]	Dec. 31, 2012 CECONY [Member]	Dec. 31, 2011 Commodity [Member]	Dec. 31, 2012 Commodity [Member] Con Edison [Member]	Dec. 31, 2012 Commodity [Member] Con Edison [Member] Derivatives Assets [Member]	Dec. 31, 2012 Commodity [Member] Con Edison [Member] Derivatives Liabilities [Member]	Dec. 31, 2012 Commodity [Member] CECONY [Member]	Dec. 31, 2011 Commodity [Member] CECONY [Member]	Dec. 31, 2012 Commodity [Member] CECONY [Member] Derivatives Assets [Member]	Dec. 31, 2012 Commodity [Member] CECONY [Member] Derivatives Liabilities [Member]	Dec. 31, 2011 Other assets [Member]	Dec. 31, 2012 Other assets [Member] Con Edison [Member]	Dec. 31, 2012 Other assets [Member] Con Edison [Member] Derivatives Assets [Member]	Dec. 31, 2012 Other assets [Member] CECONY [Member]	Dec. 31, 2011 Other assets [Member] CECONY [Member]	Dec. 31, 2012 Other assets [Member] CECONY [Member] Derivatives Assets [Member]	Dec. 31, 2011 Interest rate contract [Member]	Dec. 31, 2012 Interest rate contract [Member] Con Edison [Member]	Dec. 31, 2012 Interest rate contract [Member] Con Edison [Member] Derivatives Liabilities [Member]	Dec. 31, 2012 Interest rate contract [Member] CECONY [Member]	Dec. 31, 2012 Interest rate contract [Member] CECONY [Member] Derivatives Liabilities [Member]	Dec. 31, 2011 Level 1 [Member]	Dec. 31, 2012 Level 1 [Member] Con Edison [Member]	Dec. 31, 2012 Level 1 [Member] CECONY [Member]	Dec. 31, 2011 Level 1 [Member] CECONY [Member]	Dec. 31, 2011 Level 1 [Member] Commodity [Member]	Dec. 31, 2012 Level 1 [Member] Commodity [Member] Con Edison [Member]	Dec. 31, 2012 Level 1 [Member] Commodity [Member] Con Edison [Member] Derivatives Assets [Member]	Dec. 31, 2012 Level 1 [Member] Commodity [Member] Con Edison [Member] Derivatives Liabilities [Member]	Dec. 31, 2012 Level 1 [Member] Commodity [Member] CECONY [Member]	Dec. 31, 2011 Level 1 [Member] Commodity [Member] CECONY [Member]	Dec. 31, 2012 Level 1 [Member] Commodity [Member] CECONY [Member] Derivatives Assets [Member]	Dec. 31, 2012 Level 1 [Member] Commodity [Member] CECONY [Member] Derivatives Liabilities [Member]	Dec. 31, 2011 Level 1 [Member] Other assets [Member]	Dec. 31, 2012 Level 1 [Member] Other assets [Member] Con Edison [Member]	Dec. 31, 2012 Level 1 [Member] Other assets [Member] Con Edison [Member] Derivatives Assets [Member]	Dec. 31, 2012 Level 1 [Member] Other assets [Member] CECONY [Member]	Dec. 31, 2011 Level 1 [Member] Other assets [Member] CECONY [Member]	Dec. 31, 2012 Level 1 [Member] Other assets [Member] CECONY [Member] Derivatives Assets [Member]	Dec. 31, 2012 Level 1 [Member] Interest rate contract [Member] Con Edison [Member]	Dec. 31, 2012 Level 1 [Member] Interest rate contract [Member] Con Edison [Member] Derivatives Liabilities [Member]	Dec. 31, 2012 Level 1 [Member] Interest rate contract [Member] CECONY [Member]	Dec. 31, 2012 Level 1 [Member] Interest rate contract [Member] CECONY [Member] Derivatives Liabilities [Member]	Dec. 31, 2011 Level 2 [Member]	Dec. 31, 2012 Level 2 [Member] Con Edison [Member]	Dec. 31, 2011 Level 2 [Member] CECONY [Member]	Dec. 31, 2012 Level 2 [Member] CECONY [Member]	Dec. 31, 2011 Level 2 [Member] Commodity [Member]	Dec. 31, 2012 Level 2 [Member] Commodity [Member] Con Edison [Member]	Dec. 31, 2012 Level 2 [Member] Commodity [Member] Con Edison [Member] Derivatives Assets [Member]	Dec. 31, 2012 Level 2 [Member] Commodity [Member] Con Edison [Member] Derivatives Liabilities [Member]	Dec. 31, 2012 Level 2 [Member] Commodity [Member] CECONY [Member]	Dec. 31, 2011 Level 2 [Member] Commodity [Member] CECONY [Member]	Dec. 31, 2012 Level 2 [Member] Commodity [Member] CECONY [Member] Derivatives Assets [Member]	Dec. 31, 2012 Level 2 [Member] Commodity [Member] CECONY [Member] Derivatives Liabilities [Member]	Dec. 31, 2012 Level 2 [Member] Other assets [Member] Con Edison [Member]	Dec. 31, 2012 Level 2 [Member] Other assets [Member] Con Edison [Member] Derivatives Assets [Member]	Dec. 31, 2012 Level 2 [Member] Other assets [Member] CECONY [Member]	Dec. 31, 2012 Level 2 [Member] Other assets [Member] CECONY [Member] Derivatives Assets [Member]	Dec. 31, 2012 Level 2 [Member] Interest rate contract [Member] Con Edison [Member]	Dec. 31, 2012 Level 2 [Member] Interest rate contract [Member] Con Edison [Member] Derivatives Liabilities [Member]	Dec. 31, 2012 Level 2 [Member] Interest rate contract [Member] CECONY [Member]	Dec. 31, 2012 Level 2 [Member] Interest rate contract [Member] CECONY [Member] Derivatives Liabilities [Member]	Dec. 31, 2011 Level 3 [Member]	Dec. 31, 2012 Level 3 [Member] Con Edison [Member]	Dec. 31, 2011 Level 3 [Member] CECONY [Member]	Dec. 31, 2012 Level 3 [Member] CECONY [Member]	Dec. 31, 2011 Level 3 [Member] Commodity [Member]	Dec. 31, 2012 Level 3 [Member] Commodity [Member] Con Edison [Member]	Dec. 31, 2012 Level 3 [Member] Commodity [Member] Con Edison [Member] Derivatives Assets [Member]	Dec. 31, 2012 Level 3 [Member] Commodity [Member] Con Edison [Member] Derivatives Liabilities [Member]	Dec. 31, 2012 Level 3 [Member] Commodity [Member] CECONY [Member]	Dec. 31, 2011 Level 3 [Member] Commodity [Member] CECONY [Member]	Dec. 31, 2012 Level 3 [Member] Commodity [Member] CECONY [Member] Derivatives Assets [Member]	Dec. 31, 2012 Level 3 [Member] Commodity [Member] CECONY [Member] Derivatives Liabilities [Member]	Dec. 31, 2011 Level 3 [Member] Other assets [Member]	Dec. 31, 2012 Level 3 [Member] Other assets [Member] Con Edison [Member] Derivatives Assets [Member]	Dec. 31, 2011 Level 3 [Member] Other assets [Member] CECONY [Member]	Dec. 31, 2012 Level 3 [Member] Other assets [Member] CECONY [Member] Derivatives Assets [Member]	Dec. 31, 2011 Level 3 [Member] Interest rate contract [Member]	Dec. 31, 2012 Level 3 [Member] Interest rate contract [Member] Con Edison [Member]	Dec. 31, 2012 Level 3 [Member] Interest rate contract [Member] Con Edison [Member] Derivatives Liabilities [Member]	Dec. 31, 2012 Level 3 [Member] Interest rate contract [Member] CECONY [Member]	Dec. 31, 2012 Level 3 [Member] Interest rate contract [Member] CECONY [Member] Derivatives Liabilities [Member]	Dec. 31, 2011 Netting Adjustments [Member]	Dec. 31, 2012 Netting Adjustments [Member] Con Edison [Member]	Dec. 31, 2012 Netting Adjustments [Member] CECONY [Member]	Dec. 31, 2011 Netting Adjustments [Member] CECONY [Member]	Dec. 31, 2011 Netting Adjustments [Member] Commodity [Member]	Dec. 31, 2012 Netting Adjustments [Member] Commodity [Member] Con Edison [Member]	Dec. 31, 2012 Netting Adjustments [Member] Commodity [Member] Con Edison [Member] Derivatives Assets [Member]	Dec. 31, 2012 Netting Adjustments [Member] Commodity [Member] Con Edison [Member] Derivatives Liabilities [Member]	Dec. 31, 2012 Netting Adjustments [Member] Commodity [Member] CECONY [Member]	Dec. 31, 2011 Netting Adjustments [Member] Commodity [Member] CECONY [Member]	Dec. 31, 2012 Netting Adjustments [Member] Commodity [Member] CECONY [Member] Derivatives Assets [Member]	Dec. 31, 2012 Netting Adjustments [Member] Commodity [Member] CECONY [Member] Derivatives Liabilities [Member]	Dec. 31, 2012 Netting Adjustments [Member] Other assets [Member] Con Edison [Member]	Dec. 31, 2012 Netting Adjustments [Member] Other assets [Member] Con Edison [Member] Derivatives Assets [Member]	Dec. 31, 2012 Netting Adjustments [Member] Other assets [Member] CECONY [Member] Derivatives Assets [Member]	Dec. 31, 2012 Netting Adjustments [Member] Interest rate contract [Member] Con Edison [Member]	Dec. 31, 2012 Netting Adjustments [Member] Interest rate contract [Member] Con Edison [Member] Derivatives Liabilities [Member]	Dec. 31, 2012 Netting Adjustments [Member] Interest rate contract [Member] CECONY [Member]	Dec. 31, 2012 Netting Adjustments [Member] Interest rate contract [Member] CECONY [Member] Derivatives Liabilities [Member]
Derivative assets:
Derivative assets					$ 70		$ 66			$ 24	$ 30		$ 175	$ 213	$ 213	$ 197	$ 166	$ 197										$ 3								$ 76	$ 106	$ 106	$ 99	$ 76	$ 99									$ 64		$ 43			$ 8	$ 8		$ 107	$ 2	$ 98	$ 3									$ 87		$ 33			$ 11	$ 10		$ 99	$ 105	$ 90	$ 95										$ (84)		$ (10)			$ 5	$ 12
Transfer in	32		31					24				18			105			95			8										9				9											26		25					13				9		105		95		8			6		6					2
Transfer out	32		31					24				18			(105)			(95)			8										2															6		6					11				9									26		25					11				9		(105)		(95)			8
Total Assets	245	279	190	227		66			30															79	106	99	76																			64	150	8	106		43			8												186	33	101	10		33			10													(84)	(10)	12	5		(10)			12
Derivative liabilities:
Derivative liabilities	209		122		209	72		72	39	122		39							8	6	6			12			4	12	12		5	12	4		3											242		141		222	116		114	62	122		62					6	(2)			149		18		169	38		47		37		9					8		8			(194)			(41)	(194)	(94)		(94)	(35)	(41)		(35)
Transfer in	32		31					24				18			105			95			8										9				9											26		25					13				9		105		95		8			6		6					2
Total Liabilities	217	78	122	39																				12	12	12	4																			242	122	141	62																	157	38	18																			(194)	(94)	(35)	(41)
Transfer out	$ (32)		$ (31)					$ (24)				$ (18)			$ 105			$ 95			$ (8)										$ (2)															$ (6)		$ (6)					$ (11)				$ (9)									$ (26)		$ (25)					$ (11)				$ (9)		$ 105		$ 95			$ (8)