Fair Value Measurements - Schedule of Commodity Derivatives (Detail) (USD $)	3 Months Ended
	Mar. 31, 2013
Electricity [Member]
Financial Instruments [Line Items]
Valuation Techniques	Discounted Cash Flow
Electricity Wholesale Contract [Member]
Financial Instruments [Line Items]
Valuation Techniques	Discounted Cash Flow
Standard Offer Capacity Agreements [Member]
Financial Instruments [Line Items]
Valuation Techniques	Discounted Cash Flow
Transmission Congestion Contracts / Financial Transmission Rights [Member]
Financial Instruments [Line Items]
Valuation Techniques	Discounted Cash Flow
Minimum [Member] | Forward price escalator [Member]
Financial Instruments [Line Items]
Unobservable Inputs Range in Percentage	0.00%
Minimum [Member] | Present value factor [Member]
Financial Instruments [Line Items]
Unobservable Inputs Range in Percentage	1.66%
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%
Minimum [Member] | Discount to adjust auction prices for historical monthly realized settlements [Member]
Financial Instruments [Line Items]
Unobservable Inputs Range in Percentage	8.50%
Minimum [Member] | Inter-zonal forward price curves and for historical zonal losses [Member]
Financial Instruments [Line Items]
Unobservable Inputs Range	0.11
Minimum [Member] | Forward energy prices [Member]
Financial Instruments [Line Items]
Unobservable Inputs Range	28.00
Minimum [Member] | Forward capacity prices [Member]
Financial Instruments [Line Items]
Unobservable Inputs Range	1.50
Minimum [Member] | Forward capacity prices [Member] | Standard Offer Capacity Agreements [Member]
Financial Instruments [Line Items]
Unobservable Inputs Range	166.00
Minimum [Member] | Forward energy prices [Member]
Financial Instruments [Line Items]
Unobservable Inputs Range	33.00
Minimum [Member] | New Jersey solar renewable energy credit [Member]
Financial Instruments [Line Items]
Unobservable Inputs Range	2.50
Maximum [Member] | Forward price escalator [Member]
Financial Instruments [Line Items]
Unobservable Inputs Range in Percentage	3.00%
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%
Maximum [Member] | Discount to adjust auction prices for historical monthly realized settlements [Member]
Financial Instruments [Line Items]
Unobservable Inputs Range in Percentage	49.00%
Maximum [Member] | Inter-zonal forward price curves and for historical zonal losses [Member]
Financial Instruments [Line Items]
Unobservable Inputs Range	5.74
Maximum [Member] | Forward energy prices [Member]
Financial Instruments [Line Items]
Unobservable Inputs Range	116.00
Maximum [Member] | Forward capacity prices [Member]
Financial Instruments [Line Items]
Unobservable Inputs Range	14.20
Maximum [Member] | Forward energy prices [Member]
Financial Instruments [Line Items]
Unobservable Inputs Range	49.00
Maximum [Member] | New Jersey solar renewable energy credit [Member]
Financial Instruments [Line Items]
Unobservable Inputs Range	110.00
Level 3 [Member]
Financial Instruments [Line Items]
Fair Value of commodity derivatives	14,000,000
Level 3 [Member] | Electricity [Member]
Financial Instruments [Line Items]
Fair Value of commodity derivatives	12,000,000
Level 3 [Member] | Electricity Wholesale Contract [Member]
Financial Instruments [Line Items]
Fair Value of commodity derivatives	1,000,000
Level 3 [Member] | Standard Offer Capacity Agreements [Member]
Financial Instruments [Line Items]
Fair Value of commodity derivatives	(12,000,000)
Level 3 [Member] | Transmission Congestion Contracts / Financial Transmission Rights [Member]
Financial Instruments [Line Items]
Fair Value of commodity derivatives	13,000,000
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%
CECONY [Member] | Minimum [Member] | Discount to adjust auction prices for historical monthly realized settlements [Member]
Financial Instruments [Line Items]
Unobservable Inputs Range in Percentage	8.50%
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%
CECONY [Member] | Maximum [Member] | Discount to adjust auction prices for historical monthly realized settlements [Member]
Financial Instruments [Line Items]
Unobservable Inputs Range in Percentage	49.00%
CECONY [Member] | Level 3 [Member] | Transmission Congestion Contracts [Member]
Financial Instruments [Line Items]
Fair Value of commodity derivatives	11,000,000