Segment Information - Sales to Unaffiliated Customers and Long-Lived Assets by Geographic Areas (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Jan. 31, 2020	Oct. 31, 2019	Jul. 31, 2019	Apr. 30, 2019	Jan. 31, 2019	Oct. 31, 2018	Jul. 31, 2018	Apr. 30, 2018	Jan. 31, 2020	Jan. 31, 2019	Jan. 31, 2018
Revenues from External Customers and Long-Lived Assets [Line Items]
Net sales	$ 1,357.8	$ 1,014.6	$ 1,048.5	$ 1,003.1	$ 1,320.6	$ 1,012.4	$ 1,075.9	$ 1,033.2	$ 4,424.0	$ 4,442.1	$ 4,169.8
Long-lived assets	1,162.3				1,087.9				1,162.3	1,087.9
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Net sales									1,796.9	1,837.5	1,739.0
Long-lived assets	819.6				762.9				819.6	762.9
Japan
Revenues from External Customers and Long-Lived Assets [Line Items]
Net sales									649.8	643.0	596.3
Long-lived assets	17.9				18.9				17.9	18.9
Other countries
Revenues from External Customers and Long-Lived Assets [Line Items]
Net sales									1,977.3	1,961.6	$ 1,834.5
Long-lived assets	$ 324.8				$ 306.1				$ 324.8	$ 306.1