Financial Instruments (Unaudited) Not Designated as Hedging Instruments (Details)	Mar. 31, 2013 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)	491,000,000
Average contract price	3.57
Average market price	3.41
Maturities through	August 2013
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)	105,000
Average contract price	1,606
Average market price	1,601
Maturities through	July 2013
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)	124,000,000
Average contract price	3.57
Average market price	3.42
Maturities through	July 2013
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)	16,000,000
Average contract price	3.48
Maturities through	June 2013
Commodity Contract [Member] | Fair Value Hedging [Member] | Derivatives designated as hedging instruments [Member]
Derivative [Line Items]
Open positions (in lbs except gold in oz)	57,000,000
Average contract price	3.54
Maturities through	March 2014