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						9 Months Ended
	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Sep. 30, 2023	Sep. 30, 2022
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Net earnings available to common shareholders	$ 30.3	$ 65.2	$ 77.8	$ 111.3	$ 122.2	$ 91.6	$ 173.3	$ 325.1
Weighted-average common shares outstanding (in millions)
Weighted-average common shares outstanding - basic	49.5			51.7			50.1	52.6
Weighted-average common shares outstanding - diluted	50.1			52.3			50.7	53.3
Net earnings per share - basic	$ 0.61			$ 2.15			$ 3.46	$ 6.18
Net earnings per share - diluted	$ 0.6			$ 2.13			$ 3.42	$ 6.1
Effect of dilutive securities - share-based awards
Weighted-average common shares outstanding (in millions)
Effect of dilutive securities	0.6			0.6			0.6	0.7