Fair Value Measurements (Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended						12 Months Ended			12 Months Ended						12 Months Ended						12 Months Ended			12 Months Ended																																																																													3 Months Ended																								3 Months Ended
	Dec. 31, 2011		Mar. 31, 2012	Mar. 31, 2012 Level 1 [Member]	Dec. 31, 2011 Level 1 [Member]		Dec. 31, 2011 Level 2 [Member]		Mar. 31, 2012 Level 2 [Member]	Dec. 31, 2011 Level 3 [Member]		Mar. 31, 2012 Level 3 [Member]	Mar. 31, 2012 Netting Adjustments [Member]	Dec. 31, 2011 Netting Adjustments [Member]		Dec. 31, 2011 CECONY [Member]		Mar. 31, 2012 CECONY [Member]	Mar. 31, 2012 CECONY [Member] Level 1 [Member]	Dec. 31, 2011 CECONY [Member] Level 1 [Member]		Dec. 31, 2011 CECONY [Member] Level 2 [Member]		Mar. 31, 2012 CECONY [Member] Level 2 [Member]	Dec. 31, 2011 CECONY [Member] Level 3 [Member]		Mar. 31, 2012 CECONY [Member] Level 3 [Member]	Mar. 31, 2012 CECONY [Member] Netting Adjustments [Member]	Dec. 31, 2011 CECONY [Member] Netting Adjustments [Member]		Mar. 31, 2012 Commodity [Member]		Dec. 31, 2011 Commodity [Member]		Mar. 31, 2012 Commodity [Member] Level 1 [Member]		Dec. 31, 2011 Commodity [Member] Level 1 [Member]		Mar. 31, 2012 Commodity [Member] Level 2 [Member]		Dec. 31, 2011 Commodity [Member] Level 2 [Member]		Mar. 31, 2012 Commodity [Member] Level 3 [Member]		Dec. 31, 2011 Commodity [Member] Level 3 [Member]		Mar. 31, 2012 Commodity [Member] Netting Adjustments [Member]		Dec. 31, 2011 Commodity [Member] Netting Adjustments [Member]		Mar. 31, 2012 Commodity [Member] CECONY [Member]		Dec. 31, 2011 Commodity [Member] CECONY [Member]		Mar. 31, 2012 Commodity [Member] CECONY [Member] Level 1 [Member]		Dec. 31, 2011 Commodity [Member] CECONY [Member] Level 1 [Member]	Mar. 31, 2012 Commodity [Member] CECONY [Member] Level 2 [Member]		Dec. 31, 2011 Commodity [Member] CECONY [Member] Level 2 [Member]		Mar. 31, 2012 Commodity [Member] CECONY [Member] Level 3 [Member]		Dec. 31, 2011 Commodity [Member] CECONY [Member] Level 3 [Member]		Mar. 31, 2012 Commodity [Member] CECONY [Member] Netting Adjustments [Member]		Dec. 31, 2011 Commodity [Member] CECONY [Member] Netting Adjustments [Member]		Mar. 31, 2012 Other Assets [Member]		Dec. 31, 2011 Other Assets [Member]		Mar. 31, 2012 Other Assets [Member] Level 1 [Member]		Dec. 31, 2011 Other Assets [Member] Level 1 [Member]		Mar. 31, 2012 Other Assets [Member] Level 3 [Member]		Dec. 31, 2011 Other Assets [Member] Level 3 [Member]		Mar. 31, 2012 Other Assets [Member] CECONY [Member]		Dec. 31, 2011 Other Assets [Member] CECONY [Member]		Mar. 31, 2012 Other Assets [Member] CECONY [Member] Level 1 [Member]		Dec. 31, 2011 Other Assets [Member] CECONY [Member] Level 1 [Member]		Mar. 31, 2012 Other Assets [Member] CECONY [Member] Level 3 [Member]		Dec. 31, 2011 Other Assets [Member] CECONY [Member] Level 3 [Member]		Mar. 31, 2012 Interest Rate Contract [Member]		Dec. 31, 2011 Interest Rate Contract [Member]		Mar. 31, 2012 Interest Rate Contract [Member] Level 3 [Member]		Dec. 31, 2011 Interest Rate Contract [Member] Level 3 [Member]		Mar. 31, 2012 Derivatives Assets [Member]		Mar. 31, 2012 Derivatives Assets [Member] Level 2 [Member]		Mar. 31, 2012 Derivatives Assets [Member] Level 3 [Member]		Mar. 31, 2012 Derivatives Assets [Member] CECONY [Member]		Mar. 31, 2012 Derivatives Assets [Member] CECONY [Member] Level 2 [Member]		Mar. 31, 2012 Derivatives Assets [Member] CECONY [Member] Level 3 [Member]		Mar. 31, 2012 Derivatives Assets [Member] Other Assets [Member]		Mar. 31, 2012 Derivatives Assets [Member] Other Assets [Member] Level 1 [Member]		Mar. 31, 2012 Derivatives Assets [Member] Other Assets [Member] Level 2 [Member]		Mar. 31, 2012 Derivatives Assets [Member] Other Assets [Member] CECONY [Member]		Mar. 31, 2012 Derivatives Assets [Member] Other Assets [Member] CECONY [Member] Level 1 [Member]		Mar. 31, 2012 Derivatives Assets [Member] Other Assets [Member] CECONY [Member] Level 2 [Member]		Mar. 31, 2012 Derivatives Liabilities [Member]		Mar. 31, 2012 Derivatives Liabilities [Member] Level 2 [Member]		Mar. 31, 2012 Derivatives Liabilities [Member] Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets																															$ 69	[1]	$ 70	[1]	$ 2	[1]	$ 3	[1]	$ 86	[1]	$ 64	[1]	$ 103	[1]	$ 87	[1]	$ (122)	[1]	$ (84)	[1]	$ 26	[1]	$ 24	[1]				$ 4	[1]	$ 8	[1]	$ 13	[1]	$ 11	[1]	$ 9	[1]	$ 5	[1]	$ 188	[2]	$ 175	[2]	$ 83	[2]	$ 76	[2]	$ 105	[2]	$ 99	[2]	$ 178	[2]	$ 166	[2]	$ 83	[2]	$ 76	[2]	$ 95	[2]	$ 90	[2]																					$ 188	[2]	$ 83	[2]	$ 105	[2]	$ 178	[2]	$ 83	[2]	$ 95	[2]
Total assets	245		257	85	79		64		191	186		103	(122)	(84)		190		204	83	76		8		99	101		13	9	5
Transfer in	32	[3],[4],[5]					26	[3],[4],[5]		6	[3],[4],[5]					31	[3],[4],[5]					25	[3],[4],[5]		6	[3],[4],[5]																																																																												105	[3],[6]	105	[3],[6]			95	[3],[6]	95	[3],[6]															8	[3],[6]	8	[3],[6]
Transfer out	(32)	[3],[4],[5]					(6)	[3],[4],[5]		(26)	[3],[4],[5]					(31)	[3],[4],[5]					(6)	[3],[4],[5]		(25)	[3],[4],[5]																																																																												(105)	[3],[6]			(105)	[3],[6]	(95)	[3],[6]			(95)	[3],[6]													(8)	[3],[6]			(8)	[3],[6]
Derivative liabilities	209	[1]			12	[1]	242	[1]		149	[1]			(194)	[1]	122	[1]			4	[1]	141	[1]		18	[1]			(41)	[1]	244	[1]	209		10	[1]	12		316	[1]	222		196	[1]	169		(278)	[1]	(194)		143	[1]	122		2	[1]	4	170	[1]	122		26	[1]	37		(55)	[1]	(41)																										8	[7]	8	[7]	8	[7]	8	[7]
Total liabilities	$ 217		$ 252	$ 10	$ 12		$ 242		$ 324	$ 157		$ 196	$ (278)	$ (194)		$ 122		$ 143	$ 2	$ 4		$ 141		$ 170	$ 18		$ 26	$ (55)	$ (41)

[1] 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.

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

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

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

[5] 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.

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

[7] See Note J.