PROPERTY: (Details) (USD $)	12 Months Ended
Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Property
Total property	$ 8,406,700,000	$ 7,880,000,000
Accumulated depreciation, amortization and depletion	(3,986,800,000)	(3,785,000,000)
Total property, net	4,419,885,000	4,094,993,000	3,969,600,000
Depreciation and depletion expense	286,000,000	279,600,000	271,200,000
Buildings and equipment
Property
Total property	6,871,100,000	6,703,800,000
Construction in progress
Property
Total property	1,187,800,000	833,000,000
Mine development
Property
Total property	301,400,000	301,300,000
Total property, net	39,800,000	42,100,000
Land, other than mineral
Property
Total property	$ 46,400,000	$ 41,900,000

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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