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Asset Impairment (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
Asset Impairment (Details) - USD ($) $ in Millions	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Asset Impairment
Long-lived assets			$ 717.4
Equity method investment			183.4
Asset Impairment	$ 0.0	$ 0.0	900.8	$ 0.0
Loans Receivable, Net [Abstract]
Due from Affiliates	299.3		299.3
Australian Metallurgical Mining [Member]
Asset Impairment
Long-lived assets			527.0
Equity method investment			0.0
Asset Impairment			527.0
Impairment of Long-Lived Assets Held-for-use			230.5
Australian Thermal Mining [Member]
Asset Impairment
Long-lived assets			8.2
Equity method investment			0.0
Asset Impairment			8.2
Corporate and Other [Member]
Asset Impairment
Long-lived assets			182.2
Equity method investment			183.4
Asset Impairment			365.6
Impairment of Long-Lived Assets to be Disposed of			182.2
Australian Held for Sale [Member]
Asset Impairment
Impairment of Long-Lived Assets to be Disposed of			304.7
Investments [Member]
Asset Impairment
Equity method investment			46.6
Loans [Member]
Asset Impairment
Equity method investment			136.8
Priority Loans [Member]
Loans Receivable, Net [Abstract]
Due from Affiliates	$ 65.5		$ 65.5