Goodwill (Changes in the Carrying Amount of Goodwill) (Details) - USD ($)	3 Months Ended	6 Months Ended
	Jul. 31, 2018	Jul. 31, 2018
Goodwill [Roll Forward]
Goodwill gross, beginning of the period		$ 1,769,400,000
Less: accumulated impairment losses, beginning of the period		(149,200,000)
Goodwill net, beginning of the period		1,620,200,000
Additions arising from acquisitions during the period		71,900,000
Effect of foreign currency translation		(33,400,000)
Goodwill net, end of the period	$ 1,658,700,000	1,658,700,000
Goodwill impairment	$ 0	$ 0