Stockholders' Equity - Share Repurchases (Details) - USD ($)	3 Months Ended		6 Months Ended	12 Months Ended
	Apr. 30, 2020	Jan. 31, 2019	Apr. 30, 2020	Oct. 31, 2019	Mar. 31, 2017	Dec. 31, 2011
Stockholders' Equity Note [Abstract]
Share repurchase program, authorized amount for repurchase					$ 1,000,000,000.0	$ 500,000,000.0
Share repurchase program, common stock repurchased (in shares)	160,800		0	537,000.0
Share repurchase program, common stock repurchased	$ 47,800,000	$ 6,100,000		$ 156,100,000
Share repurchase program, average purchase price (in dollars per share)	$ 296.88
Share repurchase program, remaining authorized amount for repurchase	$ 359,700,000		$ 359,700,000