FINANCIAL INSTRUMENTS: (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Liabilities:
Long-term debt, Carrying Value	$ 4,205.2	$ 4,204.9
Long-term debt, Fair Value	4,233.5	4,088.8
Short term Investment:
Trading securities investment	267.3	202.6
Fair value measurements recurring \| Fair value as of the end of the period
Short term Investment:
Trading securities investment	267.3	202.6
Derivative:
Total assets, fair value	581.0	362.4
Fair value measurements recurring \| Fair value as of the end of the period \| Copper
Derivative:
Provisionally priced sales	221.3	53.9
Fair value measurements recurring \| Fair value as of the end of the period \| Molybdenum
Derivative:
Provisionally priced sales	86.7	100.2
Fair value measurements recurring \| Fair value as of the end of the period \| Corporate bonds
Available-for-sale debt securities:
Available-for-sale debt securities	0.4	0.4
Fair value measurements recurring \| Fair value as of the end of the period \| Asset backed securities
Available-for-sale debt securities:
Available-for-sale debt securities	0.1	0.1
Fair value measurements recurring \| Fair value as of the end of the period \| Mortgage backed securities
Available-for-sale debt securities:
Available-for-sale debt securities	5.2	5.2
Fair value measurements recurring \| Quoted prices in active markets for identical assets (Level 1)
Short term Investment:
Trading securities investment	267.3	202.6
Derivative:
Total assets, fair value	575.3	356.7
Fair value measurements recurring \| Quoted prices in active markets for identical assets (Level 1) \| Copper
Derivative:
Provisionally priced sales	221.3	53.9
Fair value measurements recurring \| Quoted prices in active markets for identical assets (Level 1) \| Molybdenum
Derivative:
Provisionally priced sales	86.7	100.2
Fair value measurements recurring \| Significant other observable inputs (Level 2)
Derivative:
Total assets, fair value	5.7	5.7
Fair value measurements recurring \| Significant other observable inputs (Level 2) \| Corporate bonds
Available-for-sale debt securities:
Available-for-sale debt securities	0.4	0.4
Fair value measurements recurring \| Significant other observable inputs (Level 2) \| Asset backed securities
Available-for-sale debt securities:
Available-for-sale debt securities	0.1	0.1
Fair value measurements recurring \| Significant other observable inputs (Level 2) \| Mortgage backed securities
Available-for-sale debt securities:
Available-for-sale debt securities	$ 5.2	$ 5.2

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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Carrying amount of long-term debt, net of unamortized discount or premium, including current and noncurrent amounts. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

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Amount of investments in debt and equity securities and other forms of securities that provide ownership interests classified as trading.

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