Fair Value Measurements - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Con Edison [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	$ 298	$ 279
Total liabilities	63	78
CECONY [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	246	227
Total liabilities	34	39
Commodity [Member] | Con Edison [Member] | Derivatives assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	60	66
Commodity [Member] | Con Edison [Member] | Derivatives liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	59	72
Commodity [Member] | CECONY [Member] | Derivatives assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	24	30
Commodity [Member] | CECONY [Member] | Derivatives liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	34	39
Other assets [Member] | Con Edison [Member] | Derivatives assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	238	213
Other assets [Member] | CECONY [Member] | Derivatives assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	222	197
Interest rate contract [Member] | Con Edison [Member] | Derivatives liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	4	6
Interest rate contract [Member] | CECONY [Member] | Derivatives liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities
Level 1 [Member] | Con Edison [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	128	106
Total liabilities	13	12
Level 1 [Member] | CECONY [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	121	99
Total liabilities	13	12
Level 1 [Member] | Commodity [Member] | Con Edison [Member] | Derivatives assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets
Level 1 [Member] | Commodity [Member] | Con Edison [Member] | Derivatives liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	13	12
Level 1 [Member] | Commodity [Member] | CECONY [Member] | Derivatives assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets
Level 1 [Member] | Commodity [Member] | CECONY [Member] | Derivatives liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	13	12
Level 1 [Member] | Other assets [Member] | Con Edison [Member] | Derivatives assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	128	106
Level 1 [Member] | Other assets [Member] | CECONY [Member] | Derivatives assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	121	99
Level 1 [Member] | Interest rate contract [Member] | Con Edison [Member] | Derivatives liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities
Level 1 [Member] | Interest rate contract [Member] | CECONY [Member] | Derivatives liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities
Level 2 [Member] | Con Edison [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	164	150
Total liabilities	107	122
Level 2 [Member] | CECONY [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	107	106
Total liabilities	50	62
Level 2 [Member] | Commodity [Member] | Con Edison [Member] | Derivatives assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	54	43
Level 2 [Member] | Commodity [Member] | Con Edison [Member] | Derivatives liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	103	116
Level 2 [Member] | Commodity [Member] | CECONY [Member] | Derivatives assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	6	8
Level 2 [Member] | Commodity [Member] | CECONY [Member] | Derivatives liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	50	62
Level 2 [Member] | Other assets [Member] | Con Edison [Member] | Derivatives assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	110	107
Level 2 [Member] | Other assets [Member] | CECONY [Member] | Derivatives assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	101	98
Level 2 [Member] | Interest rate contract [Member] | Con Edison [Member] | Derivatives liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	4	6
Level 2 [Member] | Interest rate contract [Member] | CECONY [Member] | Derivatives liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities
Level 3 [Member] | Con Edison [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	13	33
Total liabilities	19	38
Level 3 [Member] | CECONY [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	8	10
Total liabilities
Level 3 [Member] | Commodity [Member] | Con Edison [Member] | Derivatives assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	13	33
Level 3 [Member] | Commodity [Member] | Con Edison [Member] | Derivatives liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	19	38
Level 3 [Member] | Commodity [Member] | CECONY [Member] | Derivatives assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	8	10
Level 3 [Member] | Commodity [Member] | CECONY [Member] | Derivatives liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities
Level 3 [Member] | Other assets [Member] | Con Edison [Member] | Derivatives assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets
Level 3 [Member] | Other assets [Member] | CECONY [Member] | Derivatives assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets
Level 3 [Member] | Interest rate contract [Member] | Con Edison [Member] | Derivatives liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities
Level 3 [Member] | Interest rate contract [Member] | CECONY [Member] | Derivatives liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities
Netting Adjustments [Member] | Con Edison [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	(7)	(10)
Total liabilities	(76)	(94)
Netting Adjustments [Member] | CECONY [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	10	12
Total liabilities	(29)	(35)
Netting Adjustments [Member] | Commodity [Member] | Con Edison [Member] | Derivatives assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	(7)	(10)
Netting Adjustments [Member] | Commodity [Member] | Con Edison [Member] | Derivatives liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	(76)	(94)
Netting Adjustments [Member] | Commodity [Member] | CECONY [Member] | Derivatives assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	10	12
Netting Adjustments [Member] | Commodity [Member] | CECONY [Member] | Derivatives liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities	(29)	(35)
Netting Adjustments [Member] | Other assets [Member] | Con Edison [Member] | Derivatives assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets
Netting Adjustments [Member] | Other assets [Member] | CECONY [Member] | Derivatives assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets
Netting Adjustments [Member] | Interest rate contract [Member] | Con Edison [Member] | Derivatives liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities
Netting Adjustments [Member] | Interest rate contract [Member] | CECONY [Member] | Derivatives liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities