Other Financial Statement Details - Property, Plant and Equipment (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Mar. 31, 2019
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, gross	$ 2,978.0		$ 2,978.0		$ 2,945.7
Less accumulated depreciation and amortization	2,041.0		2,041.0		1,949.0
Total property, plant and equipment, net	937.0		937.0		996.7
Depreciation	39.5	$ 47.2	85.7	$ 85.2
Land
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, gross	83.4		83.4		83.4
Building and building improvements
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, gross	653.0		653.0		647.6
Machinery and equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, gross	2,128.0		2,128.0		2,095.5
Projects in process
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, gross	$ 113.6		$ 113.6		$ 119.2