Net Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Net earnings available to common shareholders	$ 158.0	$ 137.7	$ 398.4	$ 329.1
Weighted-average common shares outstanding (in millions)
Weighted-average common shares outstanding - basic (in shares)	64.5	66.8	65.6	67.3
Weighted-average common shares outstanding - diluted (in shares)	65.0	67.6	66.1	68.1
Net earnings per share - basic (in dollars per share)	$ 2.45	$ 2.06	$ 6.08	$ 4.89
Net earnings per share - diluted (in dollars per share)	$ 2.43	$ 2.04	$ 6.03	$ 4.84
Share-Based Awards
Weighted-average common shares outstanding (in millions)
Antidilutive securities excluded from the calculation of net earnings per share - diluted (in shares)	0.3	0.1	0.3	0.1
Stock Options
Weighted-average common shares outstanding (in millions)
Effect of dilutive securities	0.1	0.2	0.1	0.2
Non-Stock Option Awards
Weighted-average common shares outstanding (in millions)
Effect of dilutive securities	0.4	0.6	0.4	0.6