CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	3 Months Ended
	Dec. 28, 2018	Dec. 29, 2017
Statement of Cash Flows [Abstract]
Net earnings (loss)	$ 103.9	$ (112.2)
Adjustments to reconcile net earnings (loss) to net cash provided by operating activities:
Share-based compensation expense	10.5	10.7
Depreciation	12.8	12.8
Amortization of intangible assets	4.7	6.3
Gain on sale of privately-held company	(22.0)	0.0
Deferred taxes	0.0	44.9
Loss on equity investments	2.2	0.0
Provision for doubtful accounts receivable	2.0	1.5
Other, net	(0.5)	(0.8)
Changes in assets and liabilities:
Trade and unbilled receivables	2.9	65.9
Inventories	(32.4)	(11.7)
Prepaid expenses and other assets	8.6	28.2
Accounts payable	13.5	(10.3)
Accrued liabilities and other long-term liabilities	(12.5)	125.1
Deferred revenues	47.2	18.6
Net cash provided by operating activities	140.9	179.0
Cash flows from investing activities:
Purchases of property, plant and equipment	(14.0)	(9.3)
Acquisitions, net of cash acquired	(25.5)	0.0
Sale of privately-held company	29.9
Investment in available-for-sale securities	0.0	(6.0)
Loans to CPTC	(0.5)	(4.6)
Escrow deposit	0.0	(2.6)
Investment in privately-held companies	(0.8)	(2.5)
Amounts paid to deferred compensation plan trust account	(2.5)	(1.3)
Other, net	0.3	0.7
Net cash used in investing activities	(13.1)	(25.6)
Cash flows from financing activities:
Repurchases of common stock	(34.8)	(56.7)
Proceeds from issuance of common stock to employees	22.0	24.2
Tax withholdings on vesting of equity awards	(4.4)	(0.3)
Borrowings under credit facility agreement	0.0	166.4
Repayments under credit facility agreement	0.0	(166.4)
Net repayments under the credit facility agreements with maturities less than 90 days	0.0	(10.0)
Net cash used in financing activities	(17.2)	(42.8)
Effects of exchange rate changes on cash, cash equivalents, and restricted cash	1.7	(4.0)
Net increase in cash, cash equivalents, and restricted cash	112.3	106.6
Cash, cash equivalents, and restricted cash at beginning of period	516.4	718.5
Cash, cash equivalents, and restricted cash at end of period	$ 628.7	$ 825.1