Capitalization - Additional Information (Detail)	1 Months Ended		9 Months Ended
	Aug. 31, 2015 USD ($)	Apr. 30, 2015 USD ($)	Sep. 30, 2015 USD ($) project	Sep. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)
Schedule of Capitalization [Line Items]
Proceeds from long-term debt			$ 238,000,000	$ 850,000,000
Number of solar projects securing notes | project			4
Long-term debt, fair value			$ 13,575,000,000		$ 13,998,000,000
Level 2
Schedule of Capitalization [Line Items]
Long-term debt, fair value			12,939,000,000
Level 3
Schedule of Capitalization [Line Items]
Long-term debt, fair value			636,000,000
CECONY
Schedule of Capitalization [Line Items]
Proceeds from long-term debt			0	$ 850,000,000
Long-term debt, fair value			12,385,000,000		$ 12,846,000,000
CECONY | Level 2
Schedule of Capitalization [Line Items]
Long-term debt, fair value			11,749,000,000
CECONY | Level 3
Schedule of Capitalization [Line Items]
Long-term debt, fair value			636,000,000
Tax-exempt debt			636,000,000
Secured Debt | 5.30% debentures | O&R
Schedule of Capitalization [Line Items]
Proceeds from long-term debt		$ 40,000,000
Debt instrument, interest rate (percent)		5.30%
Debt Instrument, term (in years)		10 years
Secured Debt | 4.95% debentures due 2045 | O&R
Schedule of Capitalization [Line Items]
Debt Instrument, face amount			$ 120,000,000
Debt instrument, interest rate (percent)			4.95%
Secured Debt | 2.50% debentures | O&R
Schedule of Capitalization [Line Items]
Proceeds from long-term debt	$ 55,000,000
Debt instrument, interest rate (percent)	2.50%
Debt Instrument, term (in years)	5 years
Secured Debt | Variable Rate Tax-Exempt 20 Year Debt | O&R
Schedule of Capitalization [Line Items]
Proceeds from long-term debt	$ 44,000,000
Debt Instrument, term (in years)	20 years
Senior Notes | 3.94% Senior Notes due 2036 | Con Edison Development
Schedule of Capitalization [Line Items]
Debt Instrument, face amount			$ 118,000,000
Debt instrument, interest rate (percent)			3.94%