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, 2019	Oct. 31, 2018	Jul. 31, 2018	Apr. 30, 2018	Jan. 31, 2018	Oct. 31, 2017	Jul. 31, 2017	Apr. 30, 2017	Jan. 31, 2019	Jan. 31, 2018	Jan. 31, 2017
Revenues from External Customers and Long-Lived Assets [Line Items]
Net sales	$ 1,320.6	$ 1,012.4	$ 1,075.9	$ 1,033.2	$ 1,334.3	$ 976.2	$ 959.7	$ 899.6	$ 4,442.1	$ 4,169.8	$ 4,001.8
Long-lived assets	1,087.9				1,047.3				1,087.9	1,047.3
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Net sales									1,837.5	1,739.0	1,691.4
Long-lived assets	762.9				724.5				762.9	724.5
Japan
Revenues from External Customers and Long-Lived Assets [Line Items]
Net sales									643.0	596.3	604.4
Long-lived assets	18.9				21.4				18.9	21.4
Other countries
Revenues from External Customers and Long-Lived Assets [Line Items]
Net sales									1,961.6	1,834.5	$ 1,706.0
Long-lived assets	$ 306.1				$ 301.4				$ 306.1	$ 301.4