Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Jul. 31, 2018	Apr. 30, 2018	Jan. 31, 2018	Oct. 31, 2017	Jul. 31, 2017	Apr. 30, 2017	Jan. 31, 2017	Oct. 31, 2016	Jul. 31, 2018	Jul. 31, 2017	Jul. 31, 2016
Earnings Per Share [Abstract]
Options excluded from the diluted net earnings per share calculation (in shares)									0.1	1.0	3.2
Net earnings for basic and diluted earnings per share computation	$ 102.4	$ 69.9	$ (52.9)	$ 60.9	$ 68.2	$ 60.1	$ 46.5	$ 58.0	$ 180.3	$ 232.8	$ 190.8
Weighted Average Number of Shares Outstanding Reconciliation [Abstract]
Weighted average common shares – basic									130.3	132.6	133.8
Dilutive impact of share-based awards									1.9	1.5	1.0
Weighted average common shares – diluted									132.2	134.1	134.8
Net earnings per share:
Net earnings per share – basic	$ 0.79	$ 0.54	$ (0.40)	$ 0.47	$ 0.52	$ 0.45	$ 0.35	$ 0.43	$ 1.38	$ 1.76	$ 1.43
Net earnings per share – diluted	$ 0.78	$ 0.53	$ (0.40)	$ 0.46	$ 0.51	$ 0.45	$ 0.35	$ 0.43	$ 1.36	$ 1.74	$ 1.42