Stock-based Compensation Expense (Options Activity) (Details) $ / shares in Units, shares in Millions, $ in Millions	9 Months Ended
	Oct. 31, 2019 USD ($) $ / shares shares
Number of Shares
Options outstanding beginning (in shares) | shares	0.8
Exercised (in shares) | shares	(0.2)
Canceled/Forfeited (in shares) | shares	(0.1)
Options outstanding ending (in shares) | shares	0.5
Options vested and exercisable (in shares) | shares	0.2
Weighted average exercise price per share
Options outstanding beginning (in dollars per share) | $ / shares	$ 23.95
Exercised (in dollars per share) | $ / shares	23.16
Canceled/Forfeited (in dollars per share) | $ / shares	21.25
Options outstanding ending (in dollars per share) | $ / shares	24.66
Vested and exercisable (in dollars per share) | $ / shares	$ 31.13
Options outstanding, weighted average remaining contractual term (in years)	6 years 8 months 12 days
Options outstanding, aggregate intrinsic value | $	$ 63.3
Options vested and exercisable, weighted average remaining contractual term (in years)	4 years
Options vested and exercisable, aggregate intrinsic value | $	$ 22.0
Stock price (in usd per share) | $ / shares	$ 147.36
Stock Options
Number of Shares
Shares available for grant (in shares) | shares	15.0