Stockholders' Equity - Stock Repurchase Program (Details) - USD ($)	1 Months Ended	3 Months Ended		6 Months Ended
	Jul. 31, 2018	Jul. 31, 2018	Jul. 31, 2017	Jul. 31, 2018	Jul. 31, 2017	May 31, 2018
Share Repurchase [Line Items]
Approved accelerated share repurchase program	$ 250,000,000	$ 250,000,000		$ 250,000,000
Payment for accelerated share repurchases	$ 250,000,000	$ 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		$ 265,900,000	$ 21,000,000	306,300,000	$ 32,500,000
2018 share repurchase program
Share Repurchase [Line Items]
Authorized repurchase amount						$ 1,000,000,000.0
Remaining authorized repurchase amount	$ 750,000,000	750,000,000		750,000,000
2016 share repurchase program
Share Repurchase [Line Items]
Authorized repurchase amount	500,000,000	500,000,000		500,000,000
Remaining authorized repurchase amount	$ 154,900,000	154,900,000		$ 154,900,000
Shares repurchased		$ 15,900,000