Other Material Contingencies - Additional Information (Detail)		1 Months Ended	6 Months Ended
	Mar. 12, 2014 building Person lawsuit	Jul. 31, 2007 Person lawsuit	Jun. 30, 2015 USD ($)	Dec. 31, 2014 USD ($)
Guarantor Obligations [Line Items]
Number of person died in steam ruptured | Person		1
Number of suits pending against the company | lawsuit		90
Estimated accrued liability for suits			$ 50,000,000
Number of buildings destroyed by fire | building	2
Insurance receivable for suits			$ 50,000,000
Number of people died in explosion and fire incident | Person	8
Number of people injured in explosion and fire incident | Person	50
Description of explosion and fire incident			On March 12, 2014, two multi-use five-story 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.
Guarantee obligations maximum exposure			$ 2,529,000,000	$ 2,547,000,000
Ownership interest, percentage				46.00%
Estimated project cost percentage			175.00%
Manhattan Explosion and Fire
Guarantor Obligations [Line Items]
Number of suits pending against the company | lawsuit	70
Other
Guarantor Obligations [Line Items]
Guarantee obligations maximum exposure			$ 30,000,000
Indemnity agreements amount			25,000,000
Electric provider obligation to Public Utility Commission of Texas			5,000,000
Construction and Operation of Solar Energy Facilities
Guarantor Obligations [Line Items]
Guarantees issued			$ 3,000,000