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, 2020	Mar. 31, 2019
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Net earnings available to common shareholders	$ 1.7	$ 53.5
Weighted-average common shares outstanding (in millions)
Weighted-average common shares outstanding - basic (in shares)	58.7	60.6
Weighted-average common shares outstanding - diluted (in shares)	59.0	61.0
Net earnings per share - basic (in dollars per share)	$ 0.03	$ 0.88
Net earnings per share - diluted (in dollars per share)	$ 0.03	$ 0.88
Effect of dilutive securities - stock options
Weighted-average common shares outstanding (in millions)
Effect of dilutive securities	0.0	0.0
Effect of other share-based awards
Weighted-average common shares outstanding (in millions)
Effect of dilutive securities	0.3	0.4