FINANCING: (Details) (USD $)			12 Months Ended			0 Months Ended			0 Months Ended	12 Months Ended	0 Months Ended	12 Months Ended		0 Months Ended			0 Months Ended		0 Months Ended						12 Months Ended			0 Months Ended	1 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 1.763% Mitsui credit agreement due 2013 T	Dec. 31, 2011 1.763% Mitsui credit agreement due 2013	Dec. 31, 2012 1.763% Mitsui credit agreement due 2013 Minimum	Jul. 31, 2005 6.375% Notes due 2015	Dec. 31, 2012 6.375% Notes due 2015	Dec. 31, 2011 6.375% Notes due 2015	Apr. 16, 2010 Fixed-rate senior unsecured notes issued April 2010 Tranche	Dec. 31, 2012 Fixed-rate senior unsecured notes issued April 2010 Minimum Agency gradation	Nov. 08, 2012 Fixed-rate senior unsecured notes issued November 2012 Tranche	Dec. 31, 2012 Fixed-rate senior unsecured notes issued November 2012	Jul. 31, 2005 Fixed-rate senior unsecured notes issued July 2005	Apr. 16, 2010 5.375% Notes due 2020	Dec. 31, 2012 5.375% Notes due 2020	Dec. 31, 2011 5.375% Notes due 2020	Nov. 08, 2012 3.50% Notes due 2022	Dec. 31, 2012 3.50% Notes due 2022	Apr. 16, 2010 6.75% Notes due 2040	Dec. 31, 2012 6.75% Notes due 2040	Dec. 31, 2011 6.75% Notes due 2040	Dec. 31, 2012 5.25% Notes due 2042	Dec. 31, 2012 9.25% Yankee bonds Series B due 2028	Dec. 31, 2011 9.25% Yankee bonds Series B due 2028	Dec. 31, 2012 9.25% Yankee bonds Series B due 2028 Minera Mexico Minimum	Dec. 31, 2012 7.50% Notes due 2035	Dec. 31, 2011 7.50% Notes due 2035	May 09, 2006 7.50% Notes issued May 2006 and due 2035	Jul. 31, 2005 7.50% Notes issued July 2005 and due 2035
FINANCING
Total debt	$ 4,213,900,000	$ 2,745,700,000	$ 10,000,000	$ 20,000,000			$ 199,600,000	$ 199,400,000							$ 398,400,000	$ 398,100,000		$ 299,000,000		$ 1,092,000,000	$ 1,092,000,000	$ 1,178,500,000	$ 51,100,000	$ 51,100,000		$ 985,300,000	$ 985,100,000
Less, current portion	(10,000,000)	(10,000,000)
Total long-term debt	4,203,863,000	2,735,732,000
Effective interest rate at the end of the period (as a percent)				2.02%
Base rate			Japanese LIBO
Basis spread on yield reference rate at issuance (as a percent)			1.25%																									2.40%	3.15%
Interest rate (as a percent)			1.763%				6.375%								5.375%			3.50%		6.75%		5.25%	9.25%			7.50%
Face amount of debt							200,000,000								400,000,000			300,000,000		1,100,000,000		1,200,000,000				1,000,000,000
Debt discount	47,300,000					1,100,000	400,000	600,000	10,300,000		22,500,000				1,600,000	1,900,000		1,000,000		8,000,000	8,000,000	21,500,000				14,700,000	14,900,000	10,800,000	5,300,000
Ratio of EBITDA to interest expense																									2.5
Volume of copper on pledged receivables (in tons)			31,000
Stockholders' equity amount required to be maintained					750,000,000
Debt issuance amount						200,000,000			1,500,000,000		1,500,000,000			400,000,000			300,000,000		1,100,000,000									400,000,000	600,000,000
Deferred cost associated with issuance of debt, included in other assets	$ 25,900,000	$ 18,800,000							$ 8,200,000		$ 7,700,000		$ 8,800,000															$ 3,200,000
Yield reference rate at issuance																												30-Year U.S. Treasury bond	30-Year U.S. Treasury bond
Number of tranches in which debt instruments are issued									2		2
Percentage of principal amount at which notes may be required to be repurchased in event of change of control in the entity												101.00%
Number of rating agencies that could cause a change of control triggering event										1
Number of decreased gradations that could cause a change of control triggering event										1