Regulatory Matters - Other Regulatory Matters - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended		1 Months Ended	9 Months Ended	1 Months Ended	9 Months Ended		9 Months Ended	1 Months Ended			9 Months Ended
	Sep. 30, 2014	Dec. 31, 2013	Jul. 31, 2014 Rockland Electric Company [Member]	Sep. 30, 2014 Rockland Electric Company [Member]	Jul. 31, 2014 Rockland Electric Company [Member] Effective August 1, 2014 [Member]	Sep. 30, 2014 CECONY [Member]	Dec. 31, 2013 CECONY [Member]	Sep. 30, 2014 Orange and Rockland Utilities, Inc. [Member]	Aug. 31, 2014 Pike County Light & Power Company [Member] Effective September 1, 2014 [Member]	Sep. 30, 2014 Pike County Light & Power Company [Member] Effective September 15, 2014 [Member]	Jul. 31, 2014 Deferred Storm Costs [Member] Rockland Electric Company [Member]	Sep. 30, 2014 Storm Damage [Member] Customer
Public Utilities, General Disclosures [Line Items]
Electric rate increases					$ 13.00					$ 1.25
Return on common equity			9.75%
Common equity ratio			50.00%
Regulatory asset	6,566.0	7,230.0				6,023.0	6,665.0				25.6
Regulatory asset recovery period				4 years
Gas rate increases									0.1
Revenues from electric	249
Revenues from gas	32
Revenues from steam service	6
Potential refund to customers	1,603
Overcharges of construction expenditures	208
Regulatory liability	36
Company recovered from related parties	16
Amount recovered for the benefit of customers	15
Additional refundable amounts applicable to customers	25
Number of customers interrupted electric distribution service												1,400,000
Response and restoration costs						500		91
Capital expenditures						$ 148		$ 15