Fair Value Measurements - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Con Edison [Member]
Derivative assets:
Total assets	$ 310	$ 279
Derivative liabilities:
Total liabilities	40	78
CECONY [Member]
Derivative assets:
Total assets	239	227
Derivative liabilities:
Total liabilities	16	39
Commodity [Member] | Con Edison [Member] | Derivatives assets [Member]
Derivative assets:
Derivative assets	89	66
Commodity [Member] | Con Edison [Member] | Derivatives liabilities [Member]
Derivative liabilities:
Derivative liabilities	35	72
Commodity [Member] | CECONY [Member] | Derivatives assets [Member]
Derivative assets:
Derivative assets	34	30
Commodity [Member] | CECONY [Member] | Derivatives liabilities [Member]
Derivative liabilities:
Derivative liabilities	16	39
Other assets [Member] | Con Edison [Member] | Derivatives assets [Member]
Derivative assets:
Derivative assets	221	213
Other assets [Member] | CECONY [Member] | Derivatives assets [Member]
Derivative assets:
Derivative assets	205	197
Interest rate contract [Member] | Con Edison [Member] | Derivatives liabilities [Member]
Derivative liabilities:
Derivative liabilities	5	6
Level 1 [Member] | Con Edison [Member]
Derivative assets:
Total assets	111	106
Derivative liabilities:
Total liabilities	8	12
Level 1 [Member] | CECONY [Member]
Derivative assets:
Total assets	104	99
Derivative liabilities:
Total liabilities	8	12
Level 1 [Member] | Commodity [Member] | Con Edison [Member] | Derivatives assets [Member]
Derivative assets:
Derivative assets	2
Level 1 [Member] | Commodity [Member] | Con Edison [Member] | Derivatives liabilities [Member]
Derivative liabilities:
Derivative liabilities	8	12
Level 1 [Member] | Commodity [Member] | CECONY [Member] | Derivatives assets [Member]
Derivative assets:
Derivative assets	2
Level 1 [Member] | Commodity [Member] | CECONY [Member] | Derivatives liabilities [Member]
Derivative liabilities:
Derivative liabilities	8	12
Level 1 [Member] | Other assets [Member] | Con Edison [Member] | Derivatives assets [Member]
Derivative assets:
Derivative assets	109	106
Level 1 [Member] | Other assets [Member] | CECONY [Member] | Derivatives assets [Member]
Derivative assets:
Derivative assets	102	99
Level 2 [Member] | Con Edison [Member]
Derivative assets:
Total assets	183	150
Derivative liabilities:
Total liabilities	77	122
Level 2 [Member] | CECONY [Member]
Derivative assets:
Total assets	122	106
Derivative liabilities:
Total liabilities	35	62
Level 2 [Member] | Commodity [Member] | Con Edison [Member] | Derivatives assets [Member]
Derivative assets:
Derivative assets	71	43
Level 2 [Member] | Commodity [Member] | Con Edison [Member] | Derivatives liabilities [Member]
Derivative liabilities:
Derivative liabilities	72	116
Level 2 [Member] | Commodity [Member] | CECONY [Member] | Derivatives assets [Member]
Derivative assets:
Derivative assets	19	8
Level 2 [Member] | Commodity [Member] | CECONY [Member] | Derivatives liabilities [Member]
Derivative liabilities:
Derivative liabilities	35	62
Level 2 [Member] | Other assets [Member] | Con Edison [Member] | Derivatives assets [Member]
Derivative assets:
Derivative assets	112	107
Level 2 [Member] | Other assets [Member] | CECONY [Member] | Derivatives assets [Member]
Derivative assets:
Derivative assets	103	98
Level 2 [Member] | Interest rate contract [Member] | Con Edison [Member] | Derivatives liabilities [Member]
Derivative liabilities:
Derivative liabilities	5	6
Level 3 [Member] | Con Edison [Member]
Derivative assets:
Total assets	36	33
Derivative liabilities:
Total liabilities	22	38
Level 3 [Member] | CECONY [Member]
Derivative assets:
Total assets	11	10
Level 3 [Member] | Commodity [Member] | Con Edison [Member] | Derivatives assets [Member]
Derivative assets:
Derivative assets	36	33
Level 3 [Member] | Commodity [Member] | Con Edison [Member] | Derivatives liabilities [Member]
Derivative liabilities:
Derivative liabilities	22	38
Level 3 [Member] | Commodity [Member] | CECONY [Member] | Derivatives assets [Member]
Derivative assets:
Derivative assets	11	10
Netting Adjustments [Member] | Con Edison [Member]
Derivative assets:
Total assets	(20)	(10)
Derivative liabilities:
Total liabilities	(67)	(94)
Netting Adjustments [Member] | CECONY [Member]
Derivative assets:
Total assets	2	12
Derivative liabilities:
Total liabilities	(27)	(35)
Netting Adjustments [Member] | Commodity [Member] | Con Edison [Member] | Derivatives assets [Member]
Derivative assets:
Derivative assets	(20)	(10)
Netting Adjustments [Member] | Commodity [Member] | Con Edison [Member] | Derivatives liabilities [Member]
Derivative liabilities:
Derivative liabilities	(67)	(94)
Netting Adjustments [Member] | Commodity [Member] | CECONY [Member] | Derivatives assets [Member]
Derivative assets:
Derivative assets	2	12
Netting Adjustments [Member] | Commodity [Member] | CECONY [Member] | Derivatives liabilities [Member]
Derivative liabilities:
Derivative liabilities	$ (27)	$ (35)