Asset Impairments and Mine Closure Costs (Narrative) (Details) $ in Millions	3 Months Ended
Mar. 31, 2016 USD ($)
Restructuring Cost and Reserve [Line Items]
Asset impairment and mine closure costs	$ 85.5
Impairment charge on investment	2.9
Kentucky [Member]
Restructuring Cost and Reserve [Line Items]
Impaired coal reserves and surface land	74.1
Severance expense	5.1
Royalty Agreements [Member]
Restructuring Cost and Reserve [Line Items]
Impairment charge	$ 3.4

The carrying amount on the books of the entity of the impaired asset to be disposed of by a method other than sale.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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The amount of impairment loss recognized in the period resulting from the write-down of the carrying amount of a finite-lived intangible asset to fair value.

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The amount of other than temporary impairment losses on investments in debt and equity securities categorized as Available-for-sale which have been recognized in earnings during the period. Such impairment losses consist of other than temporary impairments (OTTI) on equity securities, credit losses on investments in debt securities, and when the entity intends to sell an impaired debt security or it is more likely than not that the entity will be required to sell the impaired debt security before recovery of its amortized cost basis.

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Amount of restructuring charges, remediation cost, and asset impairment loss.

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Amount of expenses for special or contractual termination benefits provided to current employees involuntarily terminated under a benefit arrangement associated exit or disposal activities pursuant to an authorized plan. Excludes expenses related to one-time termination benefits, a discontinued operation or an asset retirement obligation.

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