Goodwill (Changes in the Carrying Amount of Goodwill) (Details)	3 Months Ended
	Apr. 30, 2019 USD ($)
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 (1)	(4,600,000)
Goodwill net, end of the period	2,446,200,000
Goodwill, impairment loss	$ 0