Net Earnings Per Share - Calculations of Net Earnings Per Share - Basic and Diluted (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Net earnings available to common shareholders	$ 88.8	$ 373.8	$ 382.4
Weighted-average common shares outstanding (in millions):
Weighted-average common shares outstanding - basic	49.8	52.2	54.5
Weighted average shares - diluted	50.4	52.8	55.4
Net earnings per share - basic	$ 1.78	$ 7.17	$ 7.01
Net earnings per share - diluted	$ 1.76	$ 7.08	$ 6.91
Effect of dilutive securities - stock options
Weighted-average common shares outstanding (in millions):
Effect of dilutive securities	0.0	0.0	0.2
Effect of other share-based awards
Weighted-average common shares outstanding (in millions):
Effect of dilutive securities	0.6	0.6	0.7