Impairment Charges and Mine Closure Costs (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2012
Impaired Long-Lived Assets Held and Used [Line Items]
Restructuring Charges	$ 5.1
Impairment Charge	15.4
Inventory Write-down		2.6
Impairment of Long-Lived Assets Held-for-use	142.8
Severance Costs		12.3
Defined Benefit Plan, Recognized Net Gain (Loss) Due to Settlements and Curtailments		(1.8)
Restructuring and Related Cost, Incurred Cost		523.5
Assets, Fair Value Disclosure, Nonrecurring	71.3
Productive Land [Member]
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment of Long-Lived Assets Held-for-use		403.3
Machinery and Equipment [Member]
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment of Long-Lived Assets Held-for-use		95.6
Mining Properties and Mineral Rights [Member]
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment of Intangible Assets, Finite-lived		$ 11.5