Deferred Compensation - Narrative (Details) - USD ($)	12 Months Ended
	Jan. 31, 2021	Jan. 31, 2020	Jan. 31, 2019
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Marketable securities	$ 85,000,000.0
Costs to obtain a contract	120,900,000	$ 98,800,000
Amortization of costs to obtain a contract	96,600,000	101,600,000	$ 108,800,000
Contract cost impairment loss	0	0	$ 0
Rabbi Trust
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Deferred compensation liability, current and non-current	81,000,000.0	69,000,000.0
Deferred compensation liability, current	7,300,000	5,300,000
Deferred compensation liability, non-current	73,700,000	63,700,000
Mutual funds
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Short-term trading securities	$ 81,000,000.0	$ 69,000,000.0