Summary of Significant Accounting Policies - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Summary Of Significant Accounting Policies [Line Items]
Annual aggregate depreciation allowance	$ 1,048,000,000
Impairment charges	0	0	0
Investment gains and losses recognized, time period, years	15 years
Other actuarial gains and losses recognized, time period, years	10 years
Difference between fair value and expected Market Related Value of plan assets	20.00%
Non Utility Plan [Member] | Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives, (years)	3 years
Non Utility Plan [Member] | Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives, (years)	30 years
CECONY [Member]
Summary Of Significant Accounting Policies [Line Items]
AFUDC rates	1.60%	4.00%	6.50%
Average depreciation rates	3.10%	3.20%	3.10%
Annual aggregate depreciation allowance	$ 993,000,000
CECONY [Member] | Electric Generation [Member] | Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives, (years)	5 years
CECONY [Member] | Electric Generation [Member] | Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives, (years)	85 years
CECONY [Member] | Gas [Member] | Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives, (years)	5 years
CECONY [Member] | Gas [Member] | Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives, (years)	85 years
CECONY [Member] | Steam [Member] | Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives, (years)	5 years
CECONY [Member] | Steam [Member] | Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives, (years)	80 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)	55 years
O&R [Member]
Summary Of Significant Accounting Policies [Line Items]
AFUDC rates	2.60%	5.70%	7.00%
Average depreciation rates	2.90%	2.80%	2.90%
O&R [Member] | Electric Generation [Member] | Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives, (years)	5 years
O&R [Member] | Electric Generation [Member] | Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives, (years)	75 years
O&R [Member] | Gas [Member] | Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful lives, (years)	5 years
O&R [Member] | Gas [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