Investment in Magnetation (Details) (USD $) In Millions, unless otherwise specified	1 Months Ended	3 Months Ended			6 Months Ended
	May 31, 2013	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Schedule of Equity Method Investments [Line Items]
Payments to Acquire Businesses and Interest in Affiliates					$ (50.0)	$ 0
Magnetation LLC [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage		49.90%			49.90%
Income (Loss) from Equity Method Investments		(1.2)		0	1.1	(0.4)
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity		99.2			99.2
Payments to Acquire Businesses and Interest in Affiliates	(50.0)		(147.5)
Other Commitment		$ 150.0			$ 150.0