Net Earnings Per Share - Calculations of Net Earnings Per Share - Basic and Diluted (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Net earnings	$ 62.0	$ 1.7
Weighted-average common shares outstanding (in millions)
Weighted-average common shares outstanding - basic	55.1	58.7
Weighted-average common shares outstanding - diluted	55.7	59.0
Net earnings per share – basic	$ 1.12	$ 0.03
Net earnings per share – diluted	$ 1.11	$ 0.03
Effect of dilutive securities - stock options
Weighted-average common shares outstanding (in millions)
Effect of dilutive securities	0.1	0.0
Effect of other share-based awards
Weighted-average common shares outstanding (in millions)
Effect of dilutive securities	0.5	0.3