Income Taxes (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Reconciliation of the expected statutory federal income tax provision to the Company's actual income tax provision
Expected income tax (benefit) provision at U.S. federal statutory rate		$ (257.0)	$ (73.0)	$ 480.8
Excess depletion		(72.7)	(69.4)	(70.8)
Capital loss		0	(118.1)	0
Minerals resource rent tax, net of federal tax	(77.2)	(87.4)	77.2	0
Foreign earnings provision differential		62.7	(59.6)	(91.6)
Remeasurement of foreign income tax accounts		(44.3)	7.9	(0.9)
State income taxes, net of federal tax benefit		(0.2)	(1.1)	12.3
General business tax credits		(18.9)	(17.4)	(17.8)
Changes in valuation allowance		(29.4)	521.5	15.4
Changes in tax reserves		8.8	24.5	14.7
Other, net		(9.9)	(30.2)	21.1
Total income tax (benefit) provision		$ (448.3)	$ 262.3	$ 363.2