Summary of Significant Accounting Policies Earnings Per Share (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net income (loss)	$ 94.7	$ 102.9	$ 193.9	$ 56.2	$ (20.2)	$ (14.8)	$ (34.0)	$ 0.4	$ 447.8		$ (68.6)		$ (140.5)
Numerator for basic earnings per share - income (loss) available to common stockholders									447.8		(68.6)		(140.5)
Adjustment for interest expense incurred on assumed conversions of convertible notes									14.6		0		0
Numerator for diluted earnings per share - income (loss) available to common stockholders after assumed conversion of convertible notes									$ 462.4		$ (68.6)		$ (140.5)
Denominator for basic earnings per share - weighted-average shares (a)									257,443,999	[1]	255,812,888	[1]	255,045,210	[1]
Effect of dilutive securities - stock based compensation awards									784,080		0		0
Effect of dilutive securities - convertible senior notes									35,455,956		0		0
Denominator for diluted earnings per share adjusted weighted average shares and assumed conversion of convertible notes (a)									293,684,035	[1]	255,812,888	[1]	255,045,210	[1]
Net income (loss) per share: basic (in dollars per share)	$ 0.37	$ 0.40	$ 0.76	$ 0.22	$ (0.08)	$ (0.06)	$ (0.13)	$ 0.00	$ 1.74		$ (0.27)		$ (0.55)
Earnings Per Share, Diluted (in dollars per share)	$ 0.33	$ 0.36	$ 0.67	$ 0.21	$ (0.08)	$ (0.06)	$ (0.13)	$ 0.00	$ 1.57		$ (0.27)		$ (0.55)
Total anti-dulitive common share equivalents excluded from earnings per share computations (in shares)									7,563,456		49,953,138		72,471,784
Stockbased compensation awards [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total anti-dulitive common share equivalents excluded from earnings per share computations (in shares)									7,563,456		14,543,835		16,007,624
Convertible senior notes [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total anti-dulitive common share equivalents excluded from earnings per share computations (in shares)									0		35,409,303		56,464,160

[1] In calculating earnings per share, pertinent accounting rules require that common shares owned by the Company's Employee Savings and Stock Ownership Plan that are as yet unallocated to participants in the plan be excluded from the calculation. Such shares are issued and outstanding, and have the same voting and other rights applicable to all other common shares.