Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Apr. 01, 2017	Mar. 31, 2018	Apr. 01, 2017
Statement of Comprehensive Income [Abstract]
Net (loss) income	$ (681.4)	$ 526.8	$ (274.7)	$ 613.3
Changes in foreign currency translation adjustment	10.1	3.4	15.6	(12.3)
Changes in unrealized holding gains and losses on available-for-sale securities, net of tax of $0.0 and $0.2 for the three and six months ended March 31, 2018 and $0.1 and $0.2 for the three and six months ended April 1, 2017:	0.0	0.1	0.0	2.4
Loss (gain) reclassified from accumulated other comprehensive loss to the statements of income	0.0	(2.5)	0.4	(2.4)
Changes in pension plans, net of taxes of $0.0 and $0.6 for the three and six months ended March 31, 2018	0.0	0.0	0.6	0.0
Changes in value of hedged interest rate caps, net of tax of $0.3 and $(4.6) for the three and six months ended March 31, 2018 and $0.3 and $0.7 for the three and six months ended April 1, 2017:		0.4		1.1
Loss reclassified from accumulated other comprehensive loss to the statements of operations	0.3	1.2	2.6	3.3
Other comprehensive income (loss)	11.1	2.6	15.6	(7.9)
Comprehensive (loss) income	$ (670.3)	$ 529.4	$ (259.1)	$ 605.4