Net Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Net earnings available to common shareholders	$ 117.0	$ 115.4	$ 191.4	$ 187.1
Weighted-average common shares outstanding (in millions)
Weighted-average common shares outstanding - basic (in shares)	67.4	71.6	67.5	72.2
Weighted-average common shares outstanding - diluted (in shares)	68.0	72.3	68.3	72.9
Net earnings per share - basic (in dollars per share)	$ 1.74	$ 1.61	$ 2.83	$ 2.59
Net earnings per share - diluted (in dollars per share)	$ 1.72	$ 1.60	$ 2.80	$ 2.57
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	0.4	0.1	0.4
Stock Options
Weighted-average common shares outstanding (in millions)
Effect of dilutive securities	0.2	0.3	0.2	0.3
Non-Stock Option Awards
Weighted-average common shares outstanding (in millions)
Effect of dilutive securities	0.4	0.4	0.6	0.4