Fair Value Measurements - Schedule of Commodity Derivatives (Detail) (USD $)	12 Months Ended
	Dec. 31, 2013
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Valuation Techniques	Discounted Cash Flow
Electricity [Member]
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Valuation Techniques	Discounted Cash Flow
Transmission Congestion Contracts / Financial Transmission Rights [Member]
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Valuation Techniques	Discounted Cash Flow
Minimum [Member] | Discount to Adjust Auction Prices for Inter-Zonal Forward Price Curves [Member]
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Unobservable Inputs Range in percentage	(5.80%)
Minimum [Member] | Discount to Adjust Auction Prices for Historical Monthly Realized Settlements [Member]
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Unobservable Inputs Range in percentage	(102.40%)
Minimum [Member] | Inter-Zonal Forward Price Curves and for Historical Zonal Losses [Member]
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Unobservable Inputs Range	$ (0.31)
Minimum [Member] | Forward energy prices [Member]
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Unobservable Inputs Range	27.75
Minimum [Member] | Forward capacity prices [Member]
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Unobservable Inputs Range	9.50
Maximum [Member] | Discount to Adjust Auction Prices for Inter-Zonal Forward Price Curves [Member]
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Unobservable Inputs Range in percentage	36.50%
Maximum [Member] | Discount to Adjust Auction Prices for Historical Monthly Realized Settlements [Member]
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Unobservable Inputs Range in percentage	49.10%
Maximum [Member] | Inter-Zonal Forward Price Curves and for Historical Zonal Losses [Member]
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Unobservable Inputs Range	10.25
Maximum [Member] | Forward energy prices [Member]
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Unobservable Inputs Range	124.75
Level 3 [Member]
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Fair Value of commodity derivatives	9,100,000
Level 3 [Member] | Electricity [Member]
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Fair Value of commodity derivatives	100,000
Level 3 [Member] | Transmission Congestion Contracts / Financial Transmission Rights [Member]
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Fair Value of commodity derivatives	9,000,000
CECONY [Member] | Transmission Congestion Contracts [Member]
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Valuation Techniques	Discounted Cash Flow
CECONY [Member] | Minimum [Member] | Discount to Adjust Auction Prices for Inter-Zonal Forward Price Curves [Member]
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Unobservable Inputs Range in percentage	(5.80%)
CECONY [Member] | Minimum [Member] | Discount to Adjust Auction Prices for Historical Monthly Realized Settlements [Member]
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Unobservable Inputs Range in percentage	(102.40%)
CECONY [Member] | Maximum [Member] | Discount to Adjust Auction Prices for Inter-Zonal Forward Price Curves [Member]
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Unobservable Inputs Range in percentage	36.50%
CECONY [Member] | Maximum [Member] | Discount to Adjust Auction Prices for Historical Monthly Realized Settlements [Member]
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Unobservable Inputs Range in percentage	49.10%
CECONY [Member] | Level 3 [Member] | Transmission Congestion Contracts [Member]
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Fair Value of commodity derivatives	$ 6,500,000