COMMITMENTS AND CONTINGENCIES: (Details) In Millions, unless otherwise specified	9 Months Ended		0 Months Ended			3 Months Ended		9 Months Ended			0 Months Ended	1 Months Ended	9 Months Ended		12 Months Ended	9 Months Ended			12 Months Ended
	Sep. 30, 2014 USD ($)	Sep. 30, 2013 USD ($)	Sep. 11, 2014 Buenavista del Cobre, S.A. de C.V USD ($)	Sep. 11, 2014 Buenavista del Cobre, S.A. de C.V MXN	Aug. 06, 2014 Buenavista del Cobre, S.A. de C.V m3 km	Sep. 30, 2014 Buenavista del Cobre, S.A. de C.V USD ($)	Sep. 30, 2014 Buenavista del Cobre, S.A. de C.V MXN	Sep. 30, 2014 Buenavista del Cobre, S.A. de C.V country	Sep. 30, 2014 Maximum Buenavista del Cobre, S.A. de C.V USD ($)	Sep. 30, 2014 Maximum Buenavista del Cobre, S.A. de C.V MXN	Apr. 08, 2014 Peruvian operations	Mar. 31, 2014 Peruvian operations	Sep. 30, 2014 Peruvian operations USD ($) item	Sep. 30, 2013 Peruvian operations USD ($)	Dec. 31, 2013 Peruvian operations	Sep. 30, 2014 Peruvian operations Maximum	Sep. 30, 2014 Mexican operations USD ($)	Sep. 30, 2013 Mexican operations USD ($)	Dec. 31, 2011 Mexican operations category person
Environmental costs
Environmental capital expenditure	$ 110.3	$ 105.7											$ 92.8	$ 75.4			$ 17.5	$ 30.3
Period required for ambient air monitoring as per environmental regulation															12 months
Revised air quality standards for sulfur dioxide as per new environmental regulation (in micrograms per cubic meter)																20
Air quality standards level for sulfur dioxide to be maintained when emission is excess than specified as per new environmental regulation (in micrograms per cubic meter)													80
Number of atmospheric basins established that require further attention													3
Number of months for identification of contaminated sites and around in facilities												12 months
Period for preparation of decontamination plan												24 months
Period of extension for preparation of decontamination plan												1 year
Number of days in which results of soil confirmation tests are to be presented to authorities												30 days
Period within which the plan must be reported to the government											1 year
Number of categories of collective actions																			3
Minimum number of people claiming injury due to collective action initiative in Civil Federal Procedures Code (CFPC)																			30
Volume of copper sulfate solution (in cubic meters)					40,000
Distance of pond under construction from mine (in kilometers)					10
Amount of administrative fines and sanctions (in pesos)									3	40
Amount committed to the Mexican Federal Government to establish a trust (in peso)			150	2,000
Number of countries in which riverside residents are affected by the spill								7
Amount deposited in the trust (in peso)						$ 37	500