SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Adjustments from Amounts Previously Reported (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended		6 Months Ended
	Oct. 02, 2015	Mar. 30, 2018	Mar. 31, 2017	Mar. 30, 2018	Mar. 31, 2017	Sep. 30, 2017	Sep. 29, 2017
Revenues:
Product		$ 393.8	$ 364.9	$ 759.4	$ 674.1
Service		336.1	298.3	649.0	590.6
Total revenues		729.9	663.2	1,408.4	1,264.7
Cost of revenues:
Product		264.2	246.9	488.1	453.1
Service		147.2	140.7	299.0	269.0
Total cost of revenues		411.4	387.6	787.1	722.1
Gross margin		318.5	275.6	621.3	542.6
Earnings from continuing operations before taxes		95.6	90.4	218.1	109.7
Taxes on earnings		22.4	20.9	257.1	32.2
Net earnings (loss) from continuing operations		73.2	69.5	(39.0)	77.5
Net loss from discontinued operations		0.0	(13.3)	0.0	(6.8)
Net (loss) earnings		73.2	56.2	(39.0)	70.7
Net earnings attributable to Varian		$ 73.2	$ 56.3	$ (39.1)	$ 70.2
Diluted net earnings per share from continuing operations attributable to Varian (in dollars per share)		$ 0.79	$ 0.74	$ (0.43)	$ 0.82
Assets:
Trade and unbilled receivables, net		$ 936.7		$ 936.7			$ 961.5
Inventories		433.8		433.8			417.7
Prepaid expenses and other current assets		226.4		226.4			190.3
Deferred tax assets		114.9		114.9			147.3
Liabilities and Equity:
Accrued liabilities		365.1		365.1			374.9
Deferred revenues		766.5		766.5			755.4
Other long-term liabilities		320.7		320.7			127.4
Retained earnings		$ 664.2		$ 664.2			778.6
As Previously Reported
Revenues:
Product			$ 386.1		$ 729.7
Service			268.9		537.1
Total revenues			655.0		1,266.8
Cost of revenues:
Product			254.2		478.6
Service			125.5		237.2
Total cost of revenues			379.7		715.8
Gross margin			275.3		551.0
Earnings from continuing operations before taxes			90.1		118.1
Taxes on earnings			20.8		34.3
Net earnings (loss) from continuing operations			69.3		83.8
Net loss from discontinued operations			(13.3)		(6.8)
Net (loss) earnings			56.0		77.0
Net earnings attributable to Varian			$ 56.1		$ 76.5
Diluted net earnings per share from continuing operations attributable to Varian (in dollars per share)			$ 0.74		$ 0.89
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 | Accounting Standards Update 2014-09
Revenues:
Product			$ (21.2)		$ (55.6)
Service			29.4		53.5
Total revenues			8.2		(2.1)
Cost of revenues:
Product			(7.3)		(25.5)
Service			15.2		31.8
Total cost of revenues			7.9		6.3
Gross margin			0.3		(8.4)
Earnings from continuing operations before taxes			0.3		(8.4)
Taxes on earnings			0.1		(2.1)
Net earnings (loss) from continuing operations			0.2		(6.3)
Net loss from discontinued operations			0.0		0.0
Net (loss) earnings			0.2		(6.3)
Net earnings attributable to Varian			$ 0.2		$ (6.3)
Diluted net earnings per share from continuing operations attributable to Varian (in dollars per share)			$ 0.00		$ (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