Stockholders' Equity - Share Repurchase Table (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
Jan. 31, 2020	Jan. 31, 2019	Jan. 31, 2018
Equity [Abstract]
Cost of repurchases	$ 163.4	$ 421.4	$ 99.2
Shares repurchased and retired (in shares)	1.8	3.5	1.0
Average cost per share (in usd per share)	$ 91.15	$ 121.28	$ 94.86

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

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