Tangible Equity Units (tMEDS) (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended			3 Months Ended	6 Months Ended		3 Months Ended	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	May 11, 2012	Jun. 30, 2013 Tangible Equity Units	Jun. 30, 2013 Tangible Equity Units	May 11, 2012 Tangible Equity Units	Jun. 30, 2013 Equity Component	Jun. 30, 2013 Equity Component	Jun. 30, 2013 Estimate of Fair Value	Dec. 31, 2012 Estimate of Fair Value	Dec. 31, 2012 Estimate of Fair Value tMEDS Tangible Equity Units	Jun. 30, 2013 Estimate of Fair Value tMEDS Equity Component
Tangible Equity Units (tMEDS)
Units issued (unit)								8,800,000
Unit price (usd per share)								$ 25
Fair Value Assumptions Discount Rate					11.68%
Prepaid expense						$ 0.8	$ 0.8
Cash interest paid	27.5	13.2	35.4	13.4		0.8	1.7
Debt issuance cost	0	8.2	0	8.2		0.9	1.8
Interest costs capitalized						0.6	0.6
Purchase contracts settled (usd per contract)										$ 4.3562
Minimum settlement rate, purchase contracts (percent)										95.00%
Settlement rate on or after November 11,2012 (usd per contract)										$ 4.5855
Settlement of prepaid common stock purchase contracts (in shares)									100,000	460,000
Common stock, shares issued (shares)									458,550	2,109,330
Fair value disclosure											$ 861.0	$ 870.2	$ 27.8	$ 19.5