Capitalization - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		May 31, 2012
Schedule of Capitalization [Line Items]
Common stock shares, outstanding	21,976,200		21,976,200
Percentage limitation for income available for dividends	100.00%
Rolling average calculation of income available for dividends, years	2 years
Tax-exempt debt issued, value	$ 494,000,000
Long-term debt, fair value	13,998,000,000		12,082,000,000
Tax-exempt debt	1,130,000,000		1,130,000,000
Long-term debt	12,191,000,000		10,974,000,000
Debt instrument, covenant description	Con Edison's ratio of consolidated debt to consolidated capital to exceed 0.675 to 1
Covenant principal balance amount limit	100,000,000
Level 2 [Member]
Schedule of Capitalization [Line Items]
Long-term debt, fair value	13,362,000,000
Level 3 [Member]
Schedule of Capitalization [Line Items]
Long-term debt, fair value	636,000,000
Maximum [Member]
Schedule of Capitalization [Line Items]
Ratio of consolidated debt to consolidated capital for tax exempt financing	0.675
Transition Bonds, Issued in 2004 [Member]
Schedule of Capitalization [Line Items]
Long-term debt	18,000,000		22,000,000
CECONY [Member]
Schedule of Capitalization [Line Items]
Outstanding shares of Cumulative Preferred Stock					5
Cumulative Preferred Stock, par value					$ 100
Long-term debt, fair value	12,846,000,000		10,797,000,000
Tax-exempt debt	1,086,000,000	[1]	1,086,000,000	[1]
Long-term debt	11,214,000,000	[1]	9,841,000,000	[1]
CECONY [Member] | Level 2 [Member]
Schedule of Capitalization [Line Items]
Long-term debt, fair value	12,210,000,000
CECONY [Member] | Level 3 [Member]
Schedule of Capitalization [Line Items]
Long-term debt, fair value	636,000,000
Tax-exempt debt	636,000,000
CECONY [Member] | Maximum [Member]
Schedule of Capitalization [Line Items]
Covenant principal balance amount limit	100,000,000
Ratio of consolidated debt to consolidated capital for tax exempt financing	0.65
CECONY [Member] | Minimum [Member]
Schedule of Capitalization [Line Items]
Covenant principal balance amount limit	$ 150,000,000

[1] Rates are to be reset weekly or by auction held every 35 days; December 31, 2014 rates shown.