Income and Mining Tax Benefit (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Income Tax Disclosure [Abstract]
Total income and mining taxes expenses (benefit)	$ 4.2	$ (16.0)	$ 3.0	$ (38.9)
Tax expense relating to loss on foreign exchange	0.4		0.4
Out-of-period adjustment			$ (1.8)