Summary of Significant Accounting Policies Discussion (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Summary of Significant Accounting Policies Discussion (Textuals) [Abstract]
Period considered to treat short-term, highly liquid investments as cash equivalents	three months or less
Other-than-temporary impairment losses on marketable securities	$ 4.7	$ 21.5	$ 35.5
Other-than-temporary impairment losses on equity and cost method investments	0	43.2	39.4
Recognition of tax benefits from uncertain tax positions	greater than fifty percent likelihood of being realized upon ultimate settlement
Restructuring charges for voluntary and involuntary workforce reductions	15.7	11.9
Asset impairment charges related to long-lived assets	149.7	463.6	833.6
Foreign currency remeasurement (loss) gains	(1.3)	34.1	4.8
Foreign currency translation adjustment	$ (41.0)	$ (92.7)	$ 19.1
Leasehold improvements [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life	Shorter of Useful Life or Remaining Life of Lease
Interest In Middlemount Coal Pty Limited [Member]
Property, Plant and Equipment [Line Items]
Ownership percentage of equity method investment	50.00%
Minimum [Member] | Buildings and improvements [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life	1
Minimum [Member] | Machinery and equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life	1
Maximum [Member] | Buildings and improvements [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life	37
Maximum [Member] | Machinery and equipment [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life	37