Regulatory Matters - Cecony - Gas - Additional Information (Detail) (USD $) In Millions, unless otherwise specified			12 Months Ended			12 Months Ended					12 Months Ended						12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2013 CECONY-Gas [Member]	Dec. 31, 2012 CECONY-Gas [Member]	Dec. 31, 2011 CECONY-Gas [Member]	Dec. 31, 2016 CECONY-Gas [Member] Scenario, Forecast [Member]	Dec. 31, 2015 CECONY-Gas [Member] Scenario, Forecast [Member]	Dec. 31, 2014 CECONY-Gas [Member] Scenario, Forecast [Member]	Dec. 31, 2013 CECONY-Gas [Member] Maximum [Member]	Dec. 31, 2013 CECONY-Gas [Member] Maximum [Member] 50% of earnings [Member]	Dec. 31, 2013 CECONY-Gas [Member] Minimum [Member]	Dec. 31, 2013 CECONY-Gas [Member] September 2010 [Member]	Dec. 31, 2013 CECONY-Gas [Member] Gas Distribution Revenues [Member]	Dec. 31, 2012 CECONY-Gas [Member] Gas Distribution Revenues [Member]	Dec. 31, 2011 CECONY-Gas [Member] Gas Distribution Revenues [Member]	Dec. 31, 2013 CECONY-Gas [Member] 25 Percent [Member]	Dec. 31, 2013 CECONY-Gas [Member] 15 Percent [Member]	Dec. 31, 2013 CECONY-Gas [Member] May 2010 [Member]	Dec. 31, 2013 CECONY-Gas [Member] February 2014 [Member]	Dec. 31, 2013 CECONY-Gas [Member] February 2014 [Member] Maximum [Member]	Dec. 31, 2013 CECONY-Gas [Member] February 2014 [Member] Minimum [Member]	Dec. 31, 2013 CECONY-Gas [Member] October 2010 [Member]	Dec. 31, 2013 CECONY-Gas [Member] October 2011 [Member]	Dec. 31, 2013 CECONY-Gas [Member] October 2012 [Member]	Dec. 31, 2013 CECONY-Gas [Member] September 2011 [Member]	Dec. 31, 2013 CECONY-Gas [Member] September 2012 [Member]	Dec. 31, 2013 CECONY-Gas [Member] September 2013 [Member]	Dec. 31, 2013 CECONY-Gas [Member] December 2014 [Member]	Dec. 31, 2013 CECONY-Gas [Member] December 2014 [Member] Storm Hardening [Member]	Dec. 31, 2013 CECONY-Gas [Member] December 2015 [Member]	Dec. 31, 2013 CECONY-Gas [Member] December 2015 [Member] Storm Hardening [Member]	Dec. 31, 2013 CECONY-Gas [Member] December 2016 [Member]	Dec. 31, 2013 CECONY-Gas [Member] December 2016 [Member] Storm Hardening [Member]	Dec. 31, 2013 CECONY-Gas [Member] December 31, 2016[Member]
Public Utilities, General Disclosures [Line Items]
Gas base rate increase																						$ 47.1	$ 47.9	$ 46.7
Weighted average cost of capital, percentage												7.46%																7.10%		7.13%		7.21%
Return on common equity												9.60%							9.30%
Reductions in costs																									6	4	2
Cost of long-term debt																		5.57%										5.17%		5.23%		5.39%
Common equity ratio			48.00%						50.00%									48.00%
Average base rate																									3,027	3,245	3,434	3,521		3,863		4,236
Deferred regulatory liabilities																									2,934	3,148	3,346
Deferred net regulatory liabilities	2,294.0	2,061.0	26.0		0.3								36.0	22.0	20.0										0	2.9	9.5							32.0
Percentage of revenue requirement earnings										9.90%															10.35%	10.15%	10.15%
Common equity basis points			10
Deferred regulatory asset	126	126		38
Difference in property taxes									80.00%		20.00%									90.00%	10.00%
Amount of revenues retained			64	57	70											58	65
Percentage of revenue reserve			25.00%														15.00%
Accrual of regulatory asset			33
Percentage of difference between targeted and least revenue reserve			80.00%
Potential operational penalties			12.6			56.0	44.0	33.0
Potential refund from customers			32
Decrease in annual revenue																												55
Increase in annual revenues																														39		57
Capital expenditures																												524	5	586	36	627	57
Accrued revenues																	$ 65.0