Earnings (Loss) Per Share Data (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Earnings (Loss) Per Share Reconciliation [Abstract]
Net income (loss) available to common stockholders for purposes of computing basic earnings (loss) per share	$ 156.1	$ 189.7	$ (69.5)	$ 451.1
Net income (loss) available to common stockholders for purposes of computing diluted earnings (loss) per share	$ 156.1	$ 189.7	$ (69.5)	$ 451.1
Weighted-Average Number of Shares Outstanding Reconciliation [Abstract]
Basic shares	90,806,000	93,876,000	90,777,000	94,672,000
Effect of dilution	566,000	504,000	0	477,000
Diluted	91,372,000	94,380,000	90,777,000	95,149,000
Earnings (Loss) Per Share [Abstract]
Basic earnings (loss) per share	$ 1.72	$ 2.02	$ (0.76)	$ 4.76
Diluted earnings (loss) per share	$ 1.71	$ 2.01	$ (0.76)	$ 4.74
Stock Options [Member]
Potentially Dilutive Shares Excluded from the Calculation [Abstract]
Stock options excluded as their inclusion would be anti-dilutive	0	72,000	561,746	72,000