Fair Value Measurements - Schedule of Commodity Derivatives (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2012
Con Edison [Member] | Electricity Swaps [Member]
Financial Instruments [Line Items]
Valuation Techniques	Discounted Cash Flow
Con Edison [Member] | Electricity Wholesale Contract [Member]
Financial Instruments [Line Items]
Valuation Techniques	Discounted Cash Flow
Con Edison [Member] | Standard Offer Capacity Agreements [Member]
Financial Instruments [Line Items]
Valuation Techniques	Discounted Cash Flow
Con Edison [Member] | Transmission Congestion Contracts Or Financial Transmission Rights [Member]
Financial Instruments [Line Items]
Valuation Techniques	Discounted Cash Flow
Con Edison [Member] | Minimum [Member] | Forward prices [Member]
Financial Instruments [Line Items]
Unobservable Inputs Range	22	[1]
Con Edison [Member] | Minimum [Member] | Auction prices [Member]
Financial Instruments [Line Items]
Unobservable Inputs Range	29	[2]
Con Edison [Member] | Minimum [Member] | New Jersey solar [Member]
Financial Instruments [Line Items]
Unobservable Inputs Range	85	[2]
Con Edison [Member] | Minimum [Member] | Forward capacity prices [Member]
Financial Instruments [Line Items]
Unobservable Inputs Range	166	[1]
Con Edison [Member] | Minimum [Member] | Forward price escalator [Member]
Financial Instruments [Line Items]
Unobservable Inputs Range in Percentage	0.00%	[1]
Con Edison [Member] | Minimum [Member] | Present value factor [Member]
Financial Instruments [Line Items]
Unobservable Inputs Range in Percentage	1.66%	[1]
Con Edison [Member] | Minimum [Member] | Discount to adjust auction prices for inter-zonal forward price curves [Member]
Financial Instruments [Line Items]
Unobservable Inputs Range in Percentage	17.50%	[2]
Con Edison [Member] | Minimum [Member] | Discount to adjust auction prices for historical monthly realized settlements [Member]
Financial Instruments [Line Items]
Unobservable Inputs Range in Percentage	(3.00%)	[2]
Con Edison [Member] | Minimum [Member] | Historical line loss factor [Member]
Financial Instruments [Line Items]
Unobservable Inputs Range in Percentage	8.00%	[1]
Con Edison [Member] | Maximum [Member] | Forward prices [Member]
Financial Instruments [Line Items]
Unobservable Inputs Range	64	[1]
Con Edison [Member] | Maximum [Member] | Auction prices [Member]
Financial Instruments [Line Items]
Unobservable Inputs Range	52	[2]
Con Edison [Member] | Maximum [Member] | Forward price escalator [Member]
Financial Instruments [Line Items]
Unobservable Inputs Range in Percentage	(3.00%)	[1]
Con Edison [Member] | Maximum [Member] | Discount to adjust auction prices for inter-zonal forward price curves [Member]
Financial Instruments [Line Items]
Unobservable Inputs Range in Percentage	(38.00%)	[2]
Con Edison [Member] | Maximum [Member] | Discount to adjust auction prices for historical monthly realized settlements [Member]
Financial Instruments [Line Items]
Unobservable Inputs Range in Percentage	26.50%	[2]
Con Edison [Member] | Level 3 [Member]
Financial Instruments [Line Items]
Fair Value of commodity derivatives	(3)
Con Edison [Member] | Level 3 [Member] | Electricity Swaps [Member]
Financial Instruments [Line Items]
Fair Value of commodity derivatives	(9)
Con Edison [Member] | Level 3 [Member] | Electricity Wholesale Contract [Member]
Financial Instruments [Line Items]
Fair Value of commodity derivatives	4
Con Edison [Member] | Level 3 [Member] | Standard Offer Capacity Agreements [Member]
Financial Instruments [Line Items]
Fair Value of commodity derivatives	(12)
Con Edison [Member] | Level 3 [Member] | Transmission Congestion Contracts Or Financial Transmission Rights [Member]
Financial Instruments [Line Items]
Fair Value of commodity derivatives	14
CECONY [Member] | Transmission Congestion Contracts [Member]
Financial Instruments [Line Items]
Valuation Techniques	Discounted Cash Flow
CECONY [Member] | Minimum [Member] | Discount to adjust auction prices for inter-zonal forward price curves [Member]
Financial Instruments [Line Items]
Unobservable Inputs Range in Percentage	17.50%	[2]
CECONY [Member] | Minimum [Member] | Discount to adjust auction prices for historical monthly realized settlements [Member]
Financial Instruments [Line Items]
Unobservable Inputs Range in Percentage	(3.00%)	[2]
CECONY [Member] | Maximum [Member] | Discount to adjust auction prices for inter-zonal forward price curves [Member]
Financial Instruments [Line Items]
Unobservable Inputs Range in Percentage	38.00%	[2]
CECONY [Member] | Maximum [Member] | Discount to adjust auction prices for historical monthly realized settlements [Member]
Financial Instruments [Line Items]
Unobservable Inputs Range in Percentage	26.50%	[2]
CECONY [Member] | Level 3 [Member] | Transmission Congestion Contracts [Member]
Financial Instruments [Line Items]
Fair Value of commodity derivatives	12

[1] Generally, increases/(decreases) in this input in isolation would result in a higher/(lower) fair value measurement.

[2] Generally, increases/(decreases) in this input in isolation would result in a lower/(higher) fair value measurement.