Financial Instruments (Unaudited) Not Designated as Hedging Instruments (Details)	3 Months Ended
	Mar. 31, 2015 lb
Embedded derivatives in provisional sales contracts - Copper [Member] | Derivatives not designated as hedging instruments [Member]
Derivative [Line Items]
Open positions (in lbs except gold in oz)	577,000,000
Average contract price	2.75
Average market price	2.74
Maturities through	September 2015
Embedded derivatives in provisional sales contracts - Gold [Member] | Derivatives not designated as hedging instruments [Member]
Derivative [Line Items]
Open positions (in lbs except gold in oz)	155,000
Average contract price	1,195
Average market price	1,183
Maturities through	July 2015
Embedded derivatives in provisional purchase contracts - Copper [Member] | Derivatives not designated as hedging instruments [Member]
Derivative [Line Items]
Open positions (in lbs except gold in oz)	126,000,000
Average contract price	2.68
Average market price	2.75
Maturities through	July 2015
Atlantic Copper [Member] | Copper forward contracts [Member] | Derivatives not designated as hedging instruments [Member]
Derivative [Line Items]
Open positions (in lbs except gold in oz)	36,000,000
Average contract price	2.68
Maturities through	May 2015
Copper futures and swap contracts [Member] | Fair Value Hedging [Member] | Derivatives designated as hedging instruments [Member]
Derivative [Line Items]
Open positions (in lbs except gold in oz)	55,000,000
Average contract price	2.75
Maturities through	December 2016