Fair Value Measurements (Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Detail) (USD $) In Millions, unless otherwise specified	6 Months Ended		12 Months Ended		6 Months Ended		12 Months Ended			6 Months Ended		3 Months Ended		6 Months Ended					6 Months Ended						6 Months Ended													6 Months Ended				6 Months Ended																													12 Months Ended			6 Months Ended		12 Months Ended			6 Months Ended						6 Months Ended						6 Months Ended									6 Months Ended		12 Months Ended			6 Months Ended		12 Months Ended			6 Months Ended						6 Months Ended						6 Months Ended											6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011		Jun. 30, 2012 Derivatives Assets [Member]		Dec. 31, 2011 CECONY		Jun. 30, 2012 CECONY	Jun. 30, 2012 CECONY Derivatives Assets [Member]		Jun. 30, 2012 Commodity [Member]		Jun. 30, 2012 Commodity [Member]		Jun. 30, 2011 Commodity [Member]	Dec. 31, 2011 Commodity [Member]		Jun. 30, 2012 Commodity [Member] Derivatives Liabilities [Member]		Jun. 30, 2012 Commodity [Member] CECONY		Dec. 31, 2011 Commodity [Member] CECONY		Jun. 30, 2012 Commodity [Member] CECONY Derivatives Liabilities [Member]		Jun. 30, 2012 Other Assets [Member]		Dec. 31, 2011 Other Assets [Member]		Jun. 30, 2012 Other Assets [Member] Derivatives Assets [Member]		Jun. 30, 2012 Other Assets [Member] CECONY	Dec. 31, 2011 Other Assets [Member] CECONY		Jun. 30, 2012 Other Assets [Member] CECONY Derivatives Assets [Member]		Jun. 30, 2012 Interest Rate Contract [Member]		Dec. 31, 2011 Interest Rate Contract [Member]		Jun. 30, 2012 Interest Rate Contract [Member] Derivatives Liabilities [Member]		Jun. 30, 2012 Level 1 [Member]	Dec. 31, 2011 Level 1 [Member]		Jun. 30, 2012 Level 1 [Member] CECONY	Dec. 31, 2011 Level 1 [Member] CECONY		Jun. 30, 2012 Level 1 [Member] Commodity [Member]		Dec. 31, 2011 Level 1 [Member] Commodity [Member]		Jun. 30, 2012 Level 1 [Member] Commodity [Member] Derivatives Liabilities [Member]		Jun. 30, 2012 Level 1 [Member] Commodity [Member] CECONY		Dec. 31, 2011 Level 1 [Member] Commodity [Member] CECONY	Jun. 30, 2012 Level 1 [Member] Commodity [Member] CECONY Derivatives Liabilities [Member]		Jun. 30, 2012 Level 1 [Member] Other Assets [Member]	Dec. 31, 2011 Level 1 [Member] Other Assets [Member]		Jun. 30, 2012 Level 1 [Member] Other Assets [Member] Derivatives Assets [Member]		Jun. 30, 2012 Level 1 [Member] Other Assets [Member] CECONY	Dec. 31, 2011 Level 1 [Member] Other Assets [Member] CECONY		Jun. 30, 2012 Level 1 [Member] Other Assets [Member] CECONY Derivatives Assets [Member]		Dec. 31, 2011 Level 2 [Member]		Jun. 30, 2012 Level 2 [Member]	Jun. 30, 2012 Level 2 [Member] Derivatives Assets [Member]		Dec. 31, 2011 Level 2 [Member] CECONY		Jun. 30, 2012 Level 2 [Member] CECONY	Jun. 30, 2012 Level 2 [Member] CECONY Derivatives Assets [Member]		Jun. 30, 2012 Level 2 [Member] Commodity [Member]		Dec. 31, 2011 Level 2 [Member] Commodity [Member]		Jun. 30, 2012 Level 2 [Member] Commodity [Member] Derivatives Liabilities [Member]		Jun. 30, 2012 Level 2 [Member] Commodity [Member] CECONY		Dec. 31, 2011 Level 2 [Member] Commodity [Member] CECONY		Jun. 30, 2012 Level 2 [Member] Commodity [Member] CECONY Derivatives Liabilities [Member]		Jun. 30, 2012 Level 2 [Member] Other Assets [Member]	Jun. 30, 2012 Level 2 [Member] Other Assets [Member] Derivatives Assets [Member]		Jun. 30, 2012 Level 2 [Member] Other Assets [Member] CECONY	Jun. 30, 2012 Level 2 [Member] Other Assets [Member] CECONY Derivatives Assets [Member]		Jun. 30, 2012 Level 2 [Member] Interest Rate Contract [Member]	Jun. 30, 2012 Level 2 [Member] Interest Rate Contract [Member] Derivatives Liabilities [Member]		Dec. 31, 2011 Level 3 [Member]		Jun. 30, 2012 Level 3 [Member]	Jun. 30, 2012 Level 3 [Member] Derivatives Assets [Member]		Dec. 31, 2011 Level 3 [Member] CECONY		Jun. 30, 2012 Level 3 [Member] CECONY	Jun. 30, 2012 Level 3 [Member] CECONY Derivatives Assets [Member]		Jun. 30, 2012 Level 3 [Member] Commodity [Member]		Dec. 31, 2011 Level 3 [Member] Commodity [Member]		Jun. 30, 2012 Level 3 [Member] Commodity [Member] Derivatives Liabilities [Member]		Jun. 30, 2012 Level 3 [Member] Commodity [Member] CECONY		Dec. 31, 2011 Level 3 [Member] Commodity [Member] CECONY		Jun. 30, 2012 Level 3 [Member] Commodity [Member] CECONY Derivatives Liabilities [Member]		Jun. 30, 2012 Level 3 [Member] Other Assets [Member]	Dec. 31, 2011 Level 3 [Member] Other Assets [Member]		Jun. 30, 2012 Level 3 [Member] Other Assets [Member] CECONY	Dec. 31, 2011 Level 3 [Member] Other Assets [Member] CECONY		Jun. 30, 2012 Level 3 [Member] Interest Rate Contract [Member]	Dec. 31, 2011 Level 3 [Member] Interest Rate Contract [Member]		Jun. 30, 2012 Level 3 [Member] Interest Rate Contract [Member] Derivatives Liabilities [Member]		Dec. 31, 2011 Netting Adjustments [Member]		Jun. 30, 2012 Netting Adjustments [Member] CECONY		Dec. 31, 2011 Netting Adjustments [Member] CECONY		Dec. 31, 2011 Netting Adjustments [Member] Commodity [Member]		Jun. 30, 2012 Netting Adjustments [Member] Commodity [Member] CECONY		Dec. 31, 2011 Netting Adjustments [Member] Commodity [Member] CECONY		Jun. 30, 2012 Netting Adjustments [Member] Commodity [Member] CECONY Derivatives Liabilities [Member]
Transfer in			$ 32	[1],[2],[3]			$ 31	[1],[2],[3]											$ 6	[1],[4]					$ 4	[1],[4]																$ 8	[1],[4]																												$ 26	[1],[2],[3]				$ 25	[1],[2],[3]								$ 3	[1],[4]					$ 1	[1],[4]								$ 8	[1],[4]	$ 6	[1],[2],[3]				$ 6	[1],[2],[3]								$ 3	[1],[4]					$ 3	[1],[4]
Derivative assets												62	[5]	62	[5]		70	[5]			25	[5]	24	[5]			198		175	[6]	198	[6]	183	166	[6]	183	[6]													2	[5]	3	[5]			1	[5]				96	76	[6]	96	[6]	89	76	[6]	89	[6]											63	[5]	64	[5]			11	[5]	8	[5]			(3)	102	[6]	(1)	94	[6]														65	[5]	87	[5]			10	[5]	11	[5]			105	99	[6]	95	90	[6]												(84)	[5],[7]	3	[5],[7]	5	[5],[7]
Transfer in	(93)	5			105	[1],[4]				95	[1],[4]	4		4		5											(105)	[8],[9]										8	[8]																																			105	[1],[4]				95	[1],[4]
Total assets	260		245				190		208																																			98	79		90	76																							64		165			8		105																								186		65			101		10																										(84)	[7]	3	[7]	5	[7]
Total	162		217				122		85																																			6	12		1	4																							242		200			141		112																								157		126			18		20																										(194)	[7]	(48)	[7]	(41)	[7]
Transfer out			32	[1],[2],[3]	(105)	[1],[4]	31	[1],[2],[3]		(95)	[1],[4]								6	[1],[4]					4	[1],[4]																8	[4],[5]																												6	[1],[2],[3]				6	[1],[2],[3]								3	[1],[4]					3	[1],[4]										26	[1],[2],[3]		(105)	[1],[4]	25	[1],[2],[3]		(95)	[1],[4]					3	[1],[4]					1	[1],[4]										8	[4],[5]
Derivative liabilities			$ 209	[5]			$ 122	[5]				$ 155		$ 155			$ 209		$ 155	[5]	$ 85		$ 122		$ 85	[5]												$ 7		$ 8	[10]	$ 7	[10],[5]		$ 12	[5]		$ 4	[5]	$ 6		$ 12		$ 6	[5]	$ 1		$ 4	$ 1	[5]											$ 242	[5]				$ 141	[5]				$ 193		$ 222		$ 193	[5]	$ 114		$ 122		$ 112	[5]							$ (1)	$ 7	[10],[5]	$ 149	[5]				$ 18	[5]				$ 126		$ 169		$ 126	[5]	$ 18		$ 37		$ 20	[5]							$ 8	$ 8	[10]			$ (194)	[5],[7]			$ (41)	[5],[7]	$ (194)	[7]	$ (48)	[7]	$ (41)	[7]	$ (48)	[5],[7]

[1] The Companies' policy is to recognize transfers into and transfers out of the levels at the end of the reporting period.

[2] Transferred from Level 3 to Level 2 because of availability of observable market data due to decrease in the terms of certain contracts from beyond one year as of December 31, 2010 to less than one year as of December 31, 2011.

[3] Transferred from Level 2 to Level 3 because of reassessment of the levels in the fair value hierarchy within which certain inputs fall.

[4] Transferred from Level 3 to Level 2 because of reassessment of the levels in the fair value hierarchy within which certain inputs fall. Other assets and interest rate contract were transferred as of March 31, 2012.

[5] A portion of the commodity derivatives categorized in Level 3 is valued using an internally developed model with observable inputs. The models also include some less readily observable inputs resulting in the classification of the entire contract as Level 3. See Note J.

[6] Other assets are comprised of assets such as life insurance contracts within the deferred compensation plan and non-qualified retirement plans.

[7] Amounts represent the impact of legally-enforceable master netting agreements that allow the Companies to net gain and loss positions and cash collateral held or placed with the same counterparties.

[8] Other assets and interest rate contract were transferred as of March 31, 2012.

[9] Amounts included in earnings are reported in investment and other income on the consolidated income statement.

[10] See Note J.