Fair Value (Tables)

12 Months Ended

Sep. 29, 2017

Fair Value Disclosures [Abstract]

Fair Value, Assets Measured on Recurring Basis

Assets and liabilities recorded at fair value on a recurring basis consisted of the following (in millions):     

	As of September 29, 2017								As of September 30, 2016
			Fair Value Measurements								Fair Value Measurements
	Total		Level 1		Level 2		Level 3		Total		Level 1		Level 2		Level 3
Assets
Money market funds	$	592.6	$	592.6	$	—	$	—	$	408.7	$	408.7	$	—	$	—
Auction rate security	—		—		—		—		2.3		—		—		2.3
Total	$	592.6	$	592.6	$	—	$	—	$	411.0	$	408.7	$	—	$	2.3
Liabilities
Contingent consideration liability recorded for business combinations	11.9		—		—		11.9		7.9		—		—		7.9
Total	$	11.9	$	—	$	—	$	11.9	$	7.9	$	—	$	—	$	7.9

Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation

The following table summarizes changes to the fair value of the Level 3 assets (in millions):

	Auction rate security
Balance as of September 30, 2016	$	2.3
Decreases in Level 3 assets	(2.3		)
Balance as of September 29, 2017	$	—

Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation

The following table summarizes changes to the fair value of the Level 3 liabilities (in millions):

	Contingent consideration
Balance as of September 30, 2016	$	7.9
Increases to Level 3 liabilities	10.7
Changes in fair value included in earnings	(1.3		)
Decreases of Level 3 liabilities	(5.4		)
Balance as of September 29, 2017	$	11.9