Summary of Significant Accounting Policies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Summary Of Significant Accounting Policies [Line Items]
Annual aggregate depreciation allowance	$ 935
Investment gains and losses recognized, time period, years	15
Investment gains and losses recognized, time period, years	10
Difference between fair value and expected Market Related Value of plan assets	20.00%
Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives,(years)	3 years
Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives,(years)	30 years
CECONY [Member]
Summary Of Significant Accounting Policies [Line Items]
AFDC rates	6.50%	6.90%	5.30%
Average depreciation rate	3.10%	3.10%	3.10%
Annual aggregate depreciation allowance	$ 888
CECONY [Member] | Electric [Member] | Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives,(years)	5 years
CECONY [Member] | Electric [Member] | Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives,(years)	80 years
CECONY [Member] | Gas Transmission [Member] | Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives,(years)	5 years
CECONY [Member] | Gas Transmission [Member] | Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives,(years)	85 years
CECONY [Member] | Steam Plant [Member] | Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives,(years)	5 years
CECONY [Member] | Steam Plant [Member] | Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives,(years)	70 years
CECONY [Member] | General [Member] | Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives,(years)	5 years
CECONY [Member] | General [Member] | Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives,(years)	50 years
O & R [Member]
Summary Of Significant Accounting Policies [Line Items]
AFDC rates	7.00%	6.60%	5.80%
Average depreciation rate	2.90%	2.80%	2.80%
O & R [Member] | Electric [Member] | Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives,(years)	5 years
O & R [Member] | Electric [Member] | Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives,(years)	75 years
O & R [Member] | Gas Transmission [Member] | Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives,(years)	5 years
O & R [Member] | Gas Transmission [Member] | Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives,(years)	75 years
O & R [Member] | General [Member] | Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives,(years)	5 years
O & R [Member] | General [Member] | Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives,(years)	50 years