Summary of Significant Accounting Policies - Adjustments from Amounts Previously Reported (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Sep. 28, 2018	Jun. 29, 2018	Mar. 30, 2018	Dec. 29, 2017	Sep. 29, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 30, 2016	Sep. 28, 2018	Sep. 29, 2017	Sep. 30, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Trade and unbilled receivables, net of allowance for doubtful accounts of $41.1 at September 28, 2018, and $45.9 at September 29, 2017	$ 1,009.9				$ 961.5				$ 1,009.9	$ 961.5
Inventories	438.1				417.7				438.1	417.7
Prepaid expenses and other current assets	233.3				190.3				233.3	190.3
Revenues	801.6	$ 709.1	$ 729.9	$ 678.5	721.8	$ 632.8	$ 663.2	$ 601.5	2,919.1	2,619.3	$ 2,593.7
Total cost of revenues									1,645.5	1,505.4	1,489.0
Gross margin	338.7	313.6	318.5	302.8	305.8	265.5	275.6	267.0	1,273.6	1,113.9	1,104.7
Earnings from continuing operations before taxes									452.1	303.1	432.4
Taxes on earnings									301.8	77.1	110.1
Net earnings from continuing operations	116.8	72.5	73.2	(112.2)	78.6	69.9	69.5	8.0	150.3	226.0	322.3
Net (loss) earnings from discontinued operations					0.0	0.0	(13.3)	6.5	0.0	(6.8)	77.4
Net earnings									150.3	219.2	399.7
Net earnings attributable to Varian	116.4	$ 72.6	$ 73.2	$ (112.3)	$ 78.6	$ 69.7	$ 56.3	$ 13.9	$ 149.9	$ 218.5	$ 399.3
Diluted net earnings per share from continuing operations attributable to Varian (in dollars per share)					$ 0.85	$ 0.75	$ 0.74	$ 0.08	$ 1.62	$ 2.42	$ 3.36
Deferred tax assets	102.2				$ 147.3				$ 102.2	$ 147.3
Accrued liabilities	419.7				374.9				419.7	374.9
Deferred revenues	729.7				755.4				729.7	755.4
Other long-term liabilities	324.3				127.4				324.3	127.4
Retained earnings	$ 780.4				778.6				780.4	778.6
As Previously Reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Trade and unbilled receivables, net of allowance for doubtful accounts of $41.1 at September 28, 2018, and $45.9 at September 29, 2017					823.5					823.5
Inventories					439.7					439.7
Prepaid expenses and other current assets					199.8					199.8
Revenues										2,668.2	$ 2,621.1
Total cost of revenues										1,512.6	1,508.2
Gross margin										1,155.6	1,112.9
Earnings from continuing operations before taxes										344.8	440.6
Taxes on earnings										87.7	115.3
Net earnings from continuing operations										257.1	325.3
Net (loss) earnings from discontinued operations										(6.8)	77.4
Net earnings										250.3	402.7
Net earnings attributable to Varian										$ 249.6	$ 402.3
Diluted net earnings per share from continuing operations attributable to Varian (in dollars per share)										$ 2.75	$ 3.39
Deferred tax assets					138.8					$ 138.8
Accrued liabilities					394.7					394.7
Deferred revenues					640.6					640.6
Other long-term liabilities					130.0					130.0
Retained earnings					756.0					756.0
Product
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenues									1,569.9	1,394.0	$ 1,435.9
Product and Service									1,024.4	950.9	988.5
Product | As Previously Reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenues										1,555.5	1,583.9
Product and Service										1,025.3	1,071.3
Service
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenues									1,349.2	1,225.3	1,157.8
Product and Service									$ 621.1	554.5	500.5
Service | As Previously Reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenues										1,112.7	1,037.2
Product and Service										487.3	436.9
Accounting Standards Update 2014-09 | Adjustments
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Trade and unbilled receivables, net of allowance for doubtful accounts of $41.1 at September 28, 2018, and $45.9 at September 29, 2017					138.0					138.0
Inventories					(22.0)					(22.0)
Prepaid expenses and other current assets					(9.5)					(9.5)
Revenues										(48.9)	(27.4)
Total cost of revenues										(7.2)	(19.2)
Gross margin										(41.7)	(8.2)
Earnings from continuing operations before taxes										(41.7)	(8.2)
Taxes on earnings										(10.6)	(5.2)
Net earnings from continuing operations										(31.1)	(3.0)
Net (loss) earnings from discontinued operations										0.0	0.0
Net earnings										(31.1)	(3.0)
Net earnings attributable to Varian										$ (31.1)	$ (3.0)
Diluted net earnings per share from continuing operations attributable to Varian (in dollars per share)										$ (0.33)	$ (0.03)
Deferred tax assets					8.5					$ 8.5
Accrued liabilities					(19.8)					(19.8)
Deferred revenues					114.8					114.8
Other long-term liabilities					(2.6)					(2.6)
Retained earnings					$ 22.6					22.6
Accounting Standards Update 2014-09 | Product | Adjustments
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenues										(161.5)	$ (148.0)
Product and Service										(74.4)	(82.8)
Accounting Standards Update 2014-09 | Service | Adjustments
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenues										112.6	120.6
Product and Service										$ 67.2	$ 63.6