Stock-based Compensation Expense (Options Activity) (Details) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Apr. 30, 2019 USD ($) $ / shares shares
Number of Shares
Options outstanding beginning (in shares) | shares	0.8
Exercised (in shares) | shares	(0.1)
Options outstanding ending (in shares) | shares	0.7
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	24.72
Options outstanding ending (in dollars per share) | $ / shares	23.92
Vested and exercisable (in dollars per share) | $ / shares	$ 34.91
Options outstanding, weighted average remaining contractual term	7 years 6 months
Options outstanding, aggregate intrinsic value | $	$ 115.2
Options vested and exercisable, weighted average remaining contractual term	3 years 6 months
Options vested and exercisable, aggregate intrinsic value | $	$ 22.7
Stock price (in usd per share) | $ / shares	$ 178.21
Stock Options
Number of Shares
Shares available for grant (in shares) | shares	0.0