Other Financial Statements Details - Property, Plant and Equipment (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Mar. 31, 2018
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, gross	$ 3,042.7		$ 3,042.7		$ 2,644.1
Less accumulated depreciation and amortization	2,003.0		2,003.0		1,876.2
Total property, plant and equipment, net	1,039.7		1,039.7		767.9
Depreciation	47.0	$ 32.0	132.2	$ 90.9
Land
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, gross	82.3		82.3		73.4
Building and building improvements
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, gross	634.3		634.3		508.5
Machinery and equipment
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, gross	2,197.1		2,197.1		1,943.9
Projects in process
Property, Plant and Equipment [Line Items]
Total property, plant and equipment, gross	$ 129.0		$ 129.0		$ 118.3