Regulatory Matters - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended												1 Months Ended	12 Months Ended	0 Months Ended	12 Months Ended
	Dec. 31, 2014	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2011	Jun. 30, 2014	Jun. 30, 2013	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011	Oct. 31, 2012	Oct. 31, 2011	Oct. 31, 2010	Jan. 31, 2016	Dec. 31, 2015	Nov. 01, 2015	Jun. 30, 2015	Dec. 31, 2016
Electric Transmission [Member] | CECONY [Member]
Public Utilities, General Disclosures [Line Items]
Return on common equity	9.20%	10.15%	10.15%	10.15%
Common equity ratio	48.00%	48.00%	48.00%	48.00%
Electric Transmission [Member] | O&R [Member]
Public Utilities, General Disclosures [Line Items]
Return on common equity					9.50%	9.40%
Common equity ratio					48.00%	48.00%
Gas [Member] | CECONY [Member]
Public Utilities, General Disclosures [Line Items]
Return on common equity	9.30%						9.60%	9.60%	9.60%
Common equity ratio	48.00%						48.00%	48.00%	48.00%
Gas [Member] | O&R [Member]
Public Utilities, General Disclosures [Line Items]
Return on common equity										10.40%	10.40%	10.40%
Common equity ratio										48.00%	48.00%	48.00%
Scenario, Forecast [Member] | Electric Transmission [Member] | CECONY [Member]
Public Utilities, General Disclosures [Line Items]
Electric rate increases													$ 368.0
Return on common equity													10.00%	9.20%
Common equity ratio													48.00%	48.00%
Scenario, Forecast [Member] | Electric Transmission [Member] | O&R [Member]
Public Utilities, General Disclosures [Line Items]
Electric rate increases															33.4
Return on common equity															9.75%	9.60%
Common equity ratio															48.00%	48.00%
Scenario, Forecast [Member] | Gas [Member] | CECONY [Member]
Public Utilities, General Disclosures [Line Items]
Return on common equity														9.30%			9.30%
Common equity ratio														48.00%			48.00%
Scenario, Forecast [Member] | Gas [Member] | O&R [Member]
Public Utilities, General Disclosures [Line Items]
Electric rate increases															$ 40.7
Return on common equity															9.75%
Common equity ratio															48.00%