Goodwill (Changes in the Carrying Amount of Goodwill) (Details) - USD ($)	3 Months Ended	9 Months Ended
	Oct. 31, 2019	Oct. 31, 2019
Goodwill [Roll Forward]
Goodwill gross, beginning of the period		$ 2,600,000,000.0
Less: accumulated impairment losses, beginning of the period		(149,200,000)
Goodwill net, beginning of the period		2,450,800,000
Effect of foreign currency translation, measurement period adjustments, and other		(7,200,000)
Goodwill net, end of the period	$ 2,443,600,000	2,443,600,000
Goodwill impairment loss	$ 0	$ 0