Earnings Per Share (Comparison Of Basic And Diluted Earnings Per Share) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Basic earnings (loss) per share:
Net income (loss)	$ 68.6	$ (51.6)	$ 296.1	$ 82.2
Weighted average common shares outstanding	87,102,290	90,882,511	88,691,983	93,068,088
Basic earnings (loss) per share	$ 0.79	$ (0.57)	$ 3.34	$ 0.88
Diluted earnings (loss) per share:
Net income (loss)	$ 68.6	$ (51.6)	$ 296.1	$ 82.2
Weighted average common shares outstanding	87,102,290	90,882,511	88,691,983	93,068,088
Share equivalents:
Warrants and options	819,733	0	832,656	1,071,569
RSUs and LTIP awards	656,841	0	570,017	569,276
Employee share purchase plan	24,237	0	18,950	16,047
Weighted average common shares and common share equivalents outstanding - diluted	88,603,101	90,882,511	90,113,606	94,724,980
Diluted earnings (loss) per share	$ 0.77	$ (0.57)	$ 3.29	$ 0.87