SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Adjustments from Amounts Previously Reported (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended
	Oct. 02, 2015	Dec. 29, 2017	Dec. 30, 2016	Sep. 29, 2017
Revenues:
Product		$ 365.6	$ 309.2
Service		312.9	292.3
Total revenues		678.5	601.5
Cost of revenues:
Product		223.9	206.2
Service		151.8	128.3
Total cost of revenues		375.7	334.5
Gross margin		302.8	267.0
Earnings from continuing operations before taxes		122.5	19.3
Taxes on earnings		234.7	11.3
Net earnings (loss) from continuing operations		(112.2)	8.0
Net earnings from discontinued operations		0.0	6.5
Net earnings (loss)		(112.2)	14.5
Net earnings attributable to Varian		$ (112.3)	$ 13.9
Diluted net earnings per share from continuing operations attributable to Varian (in dollars per share)		$ (1.22)	$ 0.08
Assets:
Trade and unbilled receivables, net		$ 880.1		$ 961.5
Inventories		431.4		417.7
Prepaid expenses and other current assets		206.2		190.3
Deferred tax assets		112.8		147.3
Liabilities and Equity:
Accrued liabilities		350.0		374.9
Deferred revenues		772.3		755.4
Other long-term liabilities		292.4		127.4
Retained earnings		$ 620.2		778.6
As Previously Reported
Revenues:
Product			$ 343.6
Service			268.2
Total revenues			611.8
Cost of revenues:
Product			224.4
Service			111.7
Total cost of revenues			336.1
Gross margin			275.7
Earnings from continuing operations before taxes			28.0
Taxes on earnings			13.5
Net earnings (loss) from continuing operations			14.5
Net earnings from discontinued operations			6.5
Net earnings (loss)			21.0
Net earnings attributable to Varian			$ 20.4
Diluted net earnings per share from continuing operations attributable to Varian (in dollars per share)			$ 0.15
Assets:
Trade and unbilled receivables, net				823.5
Inventories				439.7
Prepaid expenses and other current assets				199.8
Deferred tax assets				138.8
Liabilities and Equity:
Accrued liabilities				394.7
Deferred revenues				640.6
Other long-term liabilities				130.0
Retained earnings				756.0
Adjustments
Revenues:
Product			$ (34.4)
Service			24.1
Total revenues			(10.3)
Cost of revenues:
Product			(18.2)
Service			16.6
Total cost of revenues			(1.6)
Gross margin			(8.7)
Earnings from continuing operations before taxes			(8.7)
Taxes on earnings			(2.2)
Net earnings (loss) from continuing operations			(6.5)
Net earnings from discontinued operations			0.0
Net earnings (loss)			(6.5)
Net earnings attributable to Varian			$ (6.5)
Diluted net earnings per share from continuing operations attributable to Varian (in dollars per share)			$ (0.07)
Assets:
Trade and unbilled receivables, net				138.0
Inventories				(22.0)
Prepaid expenses and other current assets				(9.5)
Deferred tax assets				8.5
Liabilities and Equity:
Accrued liabilities				(19.8)
Deferred revenues				114.8
Other long-term liabilities				(2.6)
Retained earnings				22.6
Retained Earnings | Accounting Standards Update 2016-09, Forfeiture Rate [Member]
Liabilities and Equity:
Reduction to beginning retained earnings due to election to recognize forfeitures as they occur				$ 0.4
Difference between Revenue Guidance in Effect before and after Topic 606
Liabilities and Equity:
Cumulative effect of ASC 606 to retained earnings	$ 56.7