Recently Issued Accounting Pronouncements - Balance Sheet Adjustments (Details) - USD ($) $ in Millions	Sep. 30, 2018	Jun. 30, 2018	Apr. 01, 2018	Mar. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accounts receivable, net	$ 668.8		$ 518.1	$ 563.7
Inventories	836.7		471.1	476.2
Other current assets	206.5		137.0	119.8
Long-term deferred tax assets	1,715.5		1,656.5	100.2
Other assets	110.1		47.7	71.8
Accrued liabilities	481.9		248.1	229.6
Deferred income on shipments to distributors	0.0		0.0	333.8
Long-term deferred tax liability	815.4		221.5	205.8
Other long-term liabilities	265.2		239.2	240.9
Accumulated other comprehensive loss	(16.7)		(19.3)	(17.6)
Retained earnings	$ 3,159.6		$ 3,199.0	1,397.3
Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accounts receivable, net				(45.6)
Inventories				(5.1)
Other current assets				17.2
Long-term deferred tax assets				(23.1)
Other assets				0.0
Accrued liabilities				18.5
Deferred income on shipments to distributors				(333.8)
Long-term deferred tax liability				16.8
Other long-term liabilities				0.0
Accumulated other comprehensive loss				0.0
Retained earnings				241.9
Accounting Standards Update 2016-01
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accounts receivable, net				0.0
Inventories				0.0
Other current assets				0.0
Long-term deferred tax assets				0.0
Other assets				0.0
Accrued liabilities				0.0
Deferred income on shipments to distributors				0.0
Long-term deferred tax liability				0.0
Other long-term liabilities				0.0
Accumulated other comprehensive loss				(1.7)
Retained earnings				1.7
Accounting Standards Update 2016-16
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accounts receivable, net				0.0
Inventories				0.0
Other current assets				0.0
Long-term deferred tax assets		$ 1,580.0		1,579.4
Other assets		(24.1)		(24.1)
Accrued liabilities				0.0
Deferred income on shipments to distributors				0.0
Long-term deferred tax liability		(1.1)		(1.1)
Other long-term liabilities		$ (1.7)		(1.7)
Accumulated other comprehensive loss				0.0
Retained earnings				$ 1,558.1