Summary of Significant Accounting Policies Discussion (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Mar. 11, 2016	Dec. 31, 2012
Summary of Significant Accounting Policies Discussion (Textuals) [Abstract]
Stockholders' Equity, Reverse Stock Split	Pursuant to the authorization provided at a special meeting of the Company's stockholders held on September 16, 2015, the Company completed a 1-for-15 reverse stock split of the shares of the Company’s common stock on September 30, 2015 (the Reverse Stock Split). Refer to Note 1. "Summary of Significant Accounting Policies" for additional details surrounding the Reverse Stock Split.	Pursuant to the authorization provided at a special meeting of the Company's stockholders held on September 16, 2015, the Company completed a 1-for-15 reverse stock split of the shares of the Company’s common stock on September 30, 2015 (the Reverse Stock Split). As a result of the Reverse Stock Split, every 15 shares of issued and outstanding common stock were combined into one issued and outstanding share of Common Stock, without any change in the par value per share.
Common Stock, Shares Authorized	53.3
Common Stock, Par or Stated Value Per Share	$ 0.01
Line of Credit Facility, Remaining Borrowing Capacity	$ 1,200.0			$ 900.0
Cash and cash equivalents	261.3	$ 298.0	$ 444.0		$ 558.8
Debt Finance Costs, Current	$ 75.9
Period considered to treat short-term, highly liquid investments as cash equivalents	three months or less
Other-than-temporary impairment losses on marketable securities	$ 0.0	4.7	21.5
Other-than-temporary impairment losses on equity and cost method investments	$ 276.5	0.0	43.2
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	$ 23.5	15.7	11.9
Asset impairment charges related to long-lived assets	1,001.3	149.7	463.6
Foreign currency remeasurement (loss) gains	(6.4)	(1.3)	34.1
Foreign currency translation adjustment	(34.9)	(41.0)	$ (92.7)
Property, Plant and Equipment [Line Items]
Deferred Finance Costs, Net	$ 74.4	$ 64.7
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]
Summary of Significant Accounting Policies Discussion (Textuals) [Abstract]
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
Common Stock [Member]
Summary of Significant Accounting Policies Discussion (Textuals) [Abstract]
Common Stock, Shares Authorized	53.3	53.3
Common Stock, Par or Stated Value Per Share	$ 0.01	$ 0.01
Property, Plant and Equipment [Line Items]
Stock Issued During Period, Shares, Reverse Stock Splits	278.0
Common Stock, Shares, issues post reverse stock split	19.0
Stock Authorized During Period, Shares, Reverse Stock Splits		800.0
Line of Credit [Member]
Property, Plant and Equipment [Line Items]
Deferred Finance Costs, Net	$ 20.4	$ 14.0
Revolving Credit Facility [Member]
Summary of Significant Accounting Policies Discussion (Textuals) [Abstract]
Line of Credit Facility, Remaining Borrowing Capacity	940.0
Line of credit facility, maximum borrowing capacity	$ 1,650.0
6.50% Senior Notes due September 2020 [Member]
Summary of Significant Accounting Policies Discussion (Textuals) [Abstract]
Stated interest rate - percentage	6.50%
Property, Plant and Equipment [Line Items]
Debt Instrument, Periodic Payment, Interest	$ 21.1
10.00% Senior Secured Second Lien Notes Due 2022 [Member]
Summary of Significant Accounting Policies Discussion (Textuals) [Abstract]
Stated interest rate - percentage	10.00%
Property, Plant and Equipment [Line Items]
Debt Instrument, Periodic Payment, Interest	$ 50.0
6.00% Senior Notes due November 2018 [Member]
Summary of Significant Accounting Policies Discussion (Textuals) [Abstract]
Stated interest rate - percentage	6.00%
6.25% Senior Notes due November 2021 [Member]
Summary of Significant Accounting Policies Discussion (Textuals) [Abstract]
Stated interest rate - percentage	6.25%
7.875% Senior Notes [Member]
Summary of Significant Accounting Policies Discussion (Textuals) [Abstract]
Stated interest rate - percentage	7.875%