Earnings Per Share (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Oct. 31, 2020	Oct. 31, 2019	Oct. 31, 2020	Oct. 31, 2019
Earnings Per Share [Abstract]
Net earnings for basic and diluted EPS	$ 119.0	$ 78.4	$ 86.3	$ 339.9
Weighted-average shares for basic EPS (shares)	121.4	120.3	121.3	121.0
Incremental shares based upon the assumed exercise of stock options and unvested restricted stock units (shares)	0.3	0.3	0.4	0.3
Weighted-average shares for diluted EPS (shares)	121.7	120.6	121.7	121.3
Antidilutive securities excluded from computation of earnings per share (shares)	0.1	1.8	0.2	1.7