Earnings Per Share (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jul. 31, 2018	Jul. 31, 2017	Jul. 31, 2018	Jul. 31, 2017
Earnings Per Share [Abstract]
Net earnings for basic and diluted EPS	$ 144.7	$ 115.0	$ 287.0	$ 207.9
Weighted-average shares for basic EPS (in shares)	123.2	124.5	123.8	124.6
Incremental shares based upon the assumed exercise of stock options and unvested restricted stock units (in shares)	0.8	0.6	0.7	0.6
Weighted-average shares for diluted EPS (in shares)	124.0	125.1	124.5	125.2
Antidilutive securities excluded from computations of earnings per share (in shares)	0.4	0.7	0.7	0.8
Payment for accelerated share repurchases	$ 250.0		$ 250.0