Net Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Net earnings available to common shareholders	$ 137.7	$ 129.2	$ 329.1	$ 316.3
Weighted-average common shares outstanding (in millions)
Weighted-average common shares outstanding - basic (in shares)	66.8	68.4	67.3	70.9
Weighted-average common shares outstanding - diluted (in shares)	67.6	69.0	68.1	71.6
Net earnings per share - basic (in dollars per share)	$ 2.06	$ 1.89	$ 4.89	$ 4.46
Net earnings per share - diluted (in dollars per share)	$ 2.04	$ 1.87	$ 4.84	$ 4.42
Share-Based Awards
Weighted-average common shares outstanding (in millions)
Antidilutive securities excluded from the calculation of net earnings per share - diluted (in shares)	0.1	0.7	0.1	0.7
Stock Options
Weighted-average common shares outstanding (in millions)
Effect of dilutive securities (in shares)	0.2	0.2	0.2	0.2
Non-Stock Option Awards
Weighted-average common shares outstanding (in millions)
Effect of dilutive securities (in shares)	0.6	0.4	0.6	0.5