Assets with values most sensitive to near-term coal pricing, including mines with comparatively shorter remaining lives and mining-related investments.

No definition available.

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Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 45
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=68055307&loc=d3e2420-110228

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585

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Amount, after cash payment, of expenses associated with exit or disposal activities pursuant to an authorized plan and expenses resulting from the write-down of assets. Excludes expenses related to a business combination, a discontinued operation or an asset retirement obligation.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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Asset Impairment (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
Asset Impairment (Details) - USD ($) $ in Millions	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Asset Impairment
Total asset impairment		$ 14.3
Asset impairment	$ 30.5	17.2	$ 247.9	$ 1,277.8	$ 154.4
Asset realization risk	$ 1,367.6
Australian Metallurgical Mining [Member]
Asset Impairment
Asset impairment		$ 17.2
Metropolitan mine [Member]
Asset Impairment
Asset impairment			$ 193.2