Other Material Contingencies - Additional Information (Detail) (USD $)	1 Months Ended	9 Months Ended
	Jul. 31, 2007 Person	Sep. 30, 2014 People Entity Lawsuits	Dec. 31, 2013
Operating Leased Assets [Line Items]
Number of person died in steam ruptured	1
Number of suits pending against the company		90
Insurance receivable for suits		$ 50,000,000
Description of explosion and fire incident		On March 12, 2014, two multi-use five-story tall buildings located on Park Avenue between 116th and 117th Street in Manhattan were destroyed by an explosion and fire. CECONY had delivered gas to the buildings through service lines from a distribution main located below ground on Park Avenue. Eight people died and more than 48 people were injured. Additional buildings were also damaged.
Number of people died in explosion and fire incident		8
Number of people injured in explosion and fire incident		48
Guarantee obligations maximum exposure		1,418,000,000	1,331,000,000
Number of entities		2
Manhattan Explosion and Fire [Member]
Operating Leased Assets [Line Items]
Number of suits pending against the company		20
Con Edison Development [Member]
Operating Leased Assets [Line Items]
Percentage of variable interests		50.00%
Number of guaranteed payments		2
Con Edison Development [Member] | Guarantee One [Member]
Operating Leased Assets [Line Items]
Guarantee obligations maximum exposure		78,000,000
Con Edison Development [Member] | Guarantee Two [Member]
Operating Leased Assets [Line Items]
Guarantee obligations maximum exposure		69,000,000
Construction and Operation of Solar Energy Facilities [Member]
Operating Leased Assets [Line Items]
Guarantees issued		3,000,000
Other [Member]
Operating Leased Assets [Line Items]
Guarantee obligations maximum exposure		30,000,000
Estimate of maximum potential obligation		5,000,000
Indemnity agreements amount		25,000,000
Insurance Receivable [Member]
Operating Leased Assets [Line Items]
Estimated accrued liability for suits		$ 50,000,000