Stockholders' Equity - Share Repurchase Table (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
Apr. 30, 2019	Apr. 30, 2018
Equity [Abstract]
Cost of repurchases	$ 25.4	$ 40.5
Shares repurchased and retired (shares)	0.3	0.4
Average cost per share (usd per share)	$ 93.77	$ 99.48

Number of shares that have been repurchased and retired during the period.

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Period Type:	duration