Supplementary Cash Flow Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Change in working capital accounts:
Accounts receivable	$ 3.0	$ (10.7)	$ (2.9)	$ 9.5
Product inventory	3.8	(17.5)	4.4	(34.9)
Material and supplies inventory	(3.5)	(2.0)	(6.1)	(0.6)
Prepaid expenses and other current assets	(1.4)	2.8	(9.2)	0.6
Income and mining taxes receivable	3.8	(6.0)	8.4	(5.3)
Accounts payable and accrued liabilities	1.1	12.1	(6.0)	(5.7)
Income, mining and other taxes payable	(0.4)	(2.2)	(0.4)	(1.0)
Change in working capital accounts, total	6.4	(23.5)	(11.8)	(37.4)
Cash interest paid	27.5	13.2	35.4	13.4
Income and mining taxes paid, net	1.4	8.9	0.3	11.1
Investing activities
Acquisition of property, plant and equipment under the Equipment Facility	0	(3.7)	0	(3.7)
Change in capital expenditure accrual	14.0	0.1	0	20.2
Other investing adjustments	25.8	11.3	49.5	17.9
Capital leases	$ 0	$ 3.7	$ 0	$ 3.7