Stockholders' Equity - Stock Repurchase Program (Details) - USD ($)	1 Months Ended	3 Months Ended		9 Months Ended
	Jul. 31, 2018	Oct. 31, 2018	Oct. 31, 2017	Oct. 31, 2018	Oct. 31, 2017	May 31, 2018
Share Repurchase [Line Items]
Approved accelerated share repurchase program		$ 250,000,000		$ 250,000,000
Payment for accelerated share repurchases		$ 250,000,000		250,000,000
Shares initially repurchased (in shares)		1,529,286
Shares repurchased (in shares)	353,112	1,882,398
Weighted average cost per share (in dollars per share)		$ 132.81
Shares repurchased		$ 71,000,000	$ 27,700,000	377,300,000	$ 60,200,000
2018 share repurchase program
Share Repurchase [Line Items]
Authorized repurchase amount						$ 1,000,000,000.0
Remaining authorized repurchase amount		679,100,000		679,100,000
2016 share repurchase program
Share Repurchase [Line Items]
Authorized repurchase amount		500,000,000		500,000,000
Remaining authorized repurchase amount		154,900,000		$ 154,900,000
Shares repurchased		$ 15,900,000