Capitalization - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012 Y	Dec. 31, 2011
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
Tax - exempt debt issued, value	$ 494
Long-term debt, fair value	12,935	12,744
Long-term debt	10,768	10,673
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
Transition Bonds, issued in 2004 [Member]
Schedule of Capitalization [Line Items]
Long-term debt	25	29
Level 2 [Member]
Schedule of Capitalization [Line Items]
Long-term debt, fair value	12,299
Level 3 [Member]
Schedule of Capitalization [Line Items]
Long-term debt, fair value	636
CECONY [Member]
Schedule of Capitalization [Line Items]
Long-term debt, fair value	11,751	11,593
Long-term debt	9,845	9,745
CECONY [Member] | Minimum [Member]
Schedule of Capitalization [Line Items]
Covenant principal balance amount limit	100
CECONY [Member] | Maximum [Member]
Schedule of Capitalization [Line Items]
Covenant principal balance amount limit	150
CECONY [Member] | Level 2 [Member]
Schedule of Capitalization [Line Items]
Long-term debt, fair value	11,115
CECONY [Member] | Level 3 [Member]
Schedule of Capitalization [Line Items]
Long-term debt, fair value	$ 636