Tangible Equity Units (tMEDS) (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended				9 Months Ended					3 Months Ended		9 Months Ended			9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2013		Sep. 30, 2012		May 11, 2012	Sep. 30, 2013 Tangible Equity Units	Sep. 30, 2012 Tangible Equity Units	Sep. 30, 2013 Tangible Equity Units	Sep. 30, 2012 Tangible Equity Units	May 11, 2012 Tangible Equity Units	Sep. 30, 2013 Equity Component	Sep. 30, 2013 Estimate of Fair Value	Dec. 31, 2012 Estimate of Fair Value	Dec. 31, 2012 Estimate of Fair Value tMEDS Tangible Equity Units	Sep. 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										$ 0.7		$ 0.7
Cash interest paid	19.1	[1]	1.4	[1]	54.5	[1]	14.8	[1]		0.7	1.1	2.4	1.1
Debt issuance cost	0		3.0		0		11.2			0.8		2.6
Interest costs capitalized											1.2		1.8
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)															460,000
Common stock, shares issued (shares)															2,109,330
Fair value disclosure																$ 918.5	$ 870.2	$ 27.8	$ 18.9

[1] For the three and nine months ended September 30, 2013, the cash interest paid of $19.1 million and $54.5 million, respectively, had been previously capitalized related to the Company's debt, as described in Note 9. For the three and nine months ended September 30, 2012, the cash interest paid of $1.4 million and $14.8 million, respectively, had been previously capitalized related to the Company's debt, as described in Note 9.