PROPERTY: (Details) (USD $)	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Property
Total property	$ 9,412,300,000	$ 8,416,700,000
Accumulated depreciation, amortization and depletion	(4,255,600,000)	(3,986,800,000)
Total property, net	5,156,731,000	4,429,906,000	4,095,000,000
Depreciation and depletion expense	323,500,000	286,000,000	279,600,000
Buildings and equipment
Property
Total property	7,497,300,000	6,921,800,000
Construction in progress
Property
Total property	1,617,600,000	1,197,800,000
Mine development
Property
Total property	250,700,000	250,700,000
Total property, net	37,900,000	39,800,000
Land, other than mineral
Property
Total property	$ 46,700,000	$ 46,400,000

The cumulative amount of depreciation, depletion and amortization (related to property, plant and equipment, but not including land) that has been recognized in the income statement.

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Gross amount, at the balance sheet date, of long-lived physical assets used in the normal conduct of business and not intended for resale. This can include land, buildings, machinery and equipment, and other types of furniture and equipment including, but not limited to, office equipment, furniture and fixtures, and computer equipment and software.

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- Definition

Tangible assets that are held by an entity for use in the production or supply of goods and services, for rental to others, or for administrative purposes and that are expected to provide economic benefit for more than one year; net of accumulated depreciation. Examples include land, buildings, machinery and equipment, and other types of furniture and equipment including, but not limited to, office equipment, furniture and fixtures, and computer equipment and software.

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