Acquisitions And Other Investments (Consolidated Thompson Purchase Price Allocation) (Details) (USD $) In Millions	Dec. 31, 2010	Sep. 30, 2011 Consolidated Thompson [Member] Scenario, Adjustment [Member]	Sep. 30, 2011 Consolidated Thompson [Member] Scenario, Previously Reported [Member]	Sep. 30, 2011 Consolidated Thompson [Member] Scenario, Change [Member]	Sep. 30, 2011 Consolidated Thompson [Member]
Cash		$ 4,554.0	$ 4,554.0
Fair value of total consideration transferred		4,554.0	4,554.0		4,600.0
Cash		130.6	130.6
Accounts receivable		102.8	102.8
Product inventories		134.2	134.2
Other current assets		35.0	35.1	(0.1)
Mineral rights		4,450.0	4,450.0
Property, plant and equipment		1,193.4	1,193.4
Intangible assets		2.1	2.1
Total identifiable assets acquired		6,048.1	6,048.2	(0.1)
Accounts payable		(13.6)	(13.6)
Accrued liabilities		(123.6)	(130.0)	6.4
Convertible debentures		(335.7)	(335.7)
Other current liabilities		(41.8)	(41.8)
Long-term deferred tax liabilities		(856.7)	(831.5)	(25.2)
Wabush Easement		(11.2)	(11.1)	(0.1)
Senior secured notes		(125.0)	(125.0)
Capital lease obligations		(70.7)	(70.7)
Other liabilities		(14.0)	(14.0)
Total identifiable liabilities assumed		(1,592.3)	(1,573.4)	(18.9)
Total identifiable net assets acquired		4,455.8	4,474.8	(19.0)
Noncontrolling interest in Bloom Lake		(947.6)	(947.6)
Preliminary goodwill		1,045.8	1,026.8	19.0
Total net assets acquired	$ (1.7)	$ 4,554.0	$ 4,554.0

The amount of acquisition cost of a business combination allocated to convertible debentures assumed from the acquired entity.

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Business Acquisition, Purchase Price Allocation, Noncurrent Liabilities, Easement Liability

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Amount of cash paid to acquire the entity.

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The total cost of the acquired entity including the cash paid to shareholders of acquired entities, fair value of debt and equity securities issued to shareholders of acquired entities, the fair value of the liabilities assumed, and direct costs of the acquisition.

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The amount of acquisition cost of a business combination allocated to an identifiable intangible asset that will be amortized.

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The amount of acquisition cost of a business combination allocated to assets acquired.

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The total purchase price of the acquired entity. This includes cash paid to equity interest holders of the acquired entity, fair value of debt and equity securities issued to equity holders of the acquired entity, and transaction costs paid to third parties to consummate the acquisition.

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The amount of acquisition cost of a business combination allocated to capital lease obligations assumed from the acquired entity.

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The amount of cash and cash equivalents acquired in a business combination.

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The amount of acquisition cost of a business combination allocated to prepaid expenses and other current assets. Does not include amounts allocated to cash and cash equivalents, marketable securities, receivables, inventory, and assets not to be used.

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The amount of acquisition cost of a business combination allocated to receivables.

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The amount of acquisition cost of a business combination allocated to work-in-process inventory.

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The amount of acquisition cost of a business combination allocated to accounts payable of the acquired entity.

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The amount of acquisition cost of a business combination allocated to accrued expenses of the acquired entity.

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The amount of acquisition cost of a business combination allocated to other current liabilities of the acquired entity. Does not include amounts allocated to the current portion of long-term debt, accounts payable and accrued expenses.

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Amount of deferred tax assets or liabilities for the differences between the values assigned and the tax bases of assets and liabilities in a business combination, net of any valuation allowance for deferred tax assets.

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Amount of goodwill arising from a business combination, which is the excess of the cost of the acquired entity over the amounts assigned to assets acquired and liabilities assumed.

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The amount of acquisition cost of a business combination allocated to liabilities assumed.

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The amount of acquisition cost of a business combination allocated to mineral rights for acquired entities in the mining industry.

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The amount of acquisition cost of a business combination allocated to the noncurrent portion of the long-term debt assumed from the acquired entity.

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The amount of acquisition cost of a business combination allocated to other noncurrent liabilities of the acquired entity.

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The amount of acquisition cost of a business combination allocated to property, plant and equipment to be used in ongoing operations.

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This element represents the fair value of the noncontrolling interest in the acquiree at the acquisition date.

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This element represents the sum of the: (1) acquisition-date fair value of the total consideration transferred which consists of the sum of the acquisition-date fair values of the assets transferred by the acquirer, the liabilities incurred by the acquirer to former owners of the acquiree, and the equity interests issued by the acquirer and (2) the acquisition-date fair value of any equity interest in the acquiree held by the acquirer prior to the business combination (for example, a step acquisition).

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