Property, Plant, Equipment and Mineral Rights and Reserves, Impairment Charge (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Property, Plant and Equipment [Line Items]
Impairment charge	$ 59.8	$ 0.9	$ 0.1
South Africa [Member] | Mineral Rights [Member]
Property, Plant and Equipment [Line Items]
Impairment charge	36.0
South Africa [Member] | Depreciable Assets [Member]
Property, Plant and Equipment [Line Items]
Impairment charge	$ 16.3