Employee Stock Plans - Options Outstanding and Exercisable Under Employee Stock Plans (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
Oct. 02, 2020	Sep. 27, 2019
Share-based Payment Arrangement, Option, Exercise Price Range, End of Period [Abstract]
Number of Shares (in shares)	1.9	2.2
Weighted Average Remaining Contractual Term (in years)	4 years 4 months 24 days
Weighted Average Exercise Price (in dollars per share)	$ 110.79	$ 97.66
Aggregate Intrinsic Value	$ 115.8
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Number of Shares (in shares)	0.9	1.2
Weighted Average Remaining Contractual Term (in years)	3 years 3 months 18 days
Weighted Average Exercise Price (in dollars per share)	$ 93.83	$ 80.98
Aggregate Intrinsic Value	$ 68.4
Closing price (in dollars per share)	$ 171.93
$67.12 - $81.97
Share-based Payment Arrangement, Option, Exercise Price Range, End of Period [Abstract]
Range of Exercise Prices, Lower (in dollars per share)	67.12
Range of Exercise Prices, Upper (in dollars per share)	$ 81.97
Number of Shares (in shares)	0.5
Weighted Average Remaining Contractual Term (in years)	2 years 4 months 24 days
Weighted Average Exercise Price (in dollars per share)	$ 77.92
Aggregate Intrinsic Value	$ 49.7
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Number of Shares (in shares)	0.5
Weighted Average Remaining Contractual Term (in years)	2 years 4 months 24 days
Weighted Average Exercise Price (in dollars per share)	$ 77.92
Aggregate Intrinsic Value	$ 49.7
$99.26 - $110.36
Share-based Payment Arrangement, Option, Exercise Price Range, End of Period [Abstract]
Range of Exercise Prices, Lower (in dollars per share)	$ 99.26
Range of Exercise Prices, Upper (in dollars per share)	$ 110.36
Number of Shares (in shares)	0.4
Weighted Average Remaining Contractual Term (in years)	4 years 7 months 6 days
Weighted Average Exercise Price (in dollars per share)	$ 108.56
Aggregate Intrinsic Value	$ 21.2
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Number of Shares (in shares)	0.1
Weighted Average Remaining Contractual Term (in years)	5 years
Weighted Average Exercise Price (in dollars per share)	$ 107.79
Aggregate Intrinsic Value	$ 3.7
$112.82 - $118.76
Share-based Payment Arrangement, Option, Exercise Price Range, End of Period [Abstract]
Range of Exercise Prices, Lower (in dollars per share)	$ 112.82
Range of Exercise Prices, Upper (in dollars per share)	$ 118.76
Number of Shares (in shares)	0.4
Weighted Average Remaining Contractual Term (in years)	4 years 8 months 12 days
Weighted Average Exercise Price (in dollars per share)	$ 115.64
Aggregate Intrinsic Value	$ 23.8
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Number of Shares (in shares)	0.2
Weighted Average Remaining Contractual Term (in years)	4 years 3 months 18 days
Weighted Average Exercise Price (in dollars per share)	$ 113.47
Aggregate Intrinsic Value	$ 10.7
$129.97 - $146.91
Share-based Payment Arrangement, Option, Exercise Price Range, End of Period [Abstract]
Range of Exercise Prices, Lower (in dollars per share)	$ 129.97
Range of Exercise Prices, Upper (in dollars per share)	$ 146.91
Number of Shares (in shares)	0.6
Weighted Average Remaining Contractual Term (in years)	5 years 10 months 24 days
Weighted Average Exercise Price (in dollars per share)	$ 137.26
Aggregate Intrinsic Value	$ 21.1
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Number of Shares (in shares)	0.1
Weighted Average Remaining Contractual Term (in years)	5 years 4 months 24 days
Weighted Average Exercise Price (in dollars per share)	$ 131.77
Aggregate Intrinsic Value	$ 4.3

No definition available.

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAdditionalDisclosuresAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iii)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

+ References

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

+ References

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Number of options outstanding, including both vested and non-vested options.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(i)-(ii)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(i)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

- References

No definition available.

+ Details

Name:	us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeEndOfPeriodAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The floor of a customized range of exercise prices for purposes of disclosing shares potentially issuable under outstanding stock option awards on all stock option plans and other required information pertaining to awards in the customized range.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLowerRangeLimit
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

The ceiling of a customized range of exercise prices for purposes of disclosing shares potentially issuable under outstanding stock option awards on all stock option plans and other required information pertaining to awards in the customized range.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

Price of a single share of a number of saleable stocks of a company.

+ References

No definition available.

+ Details

Name:	us-gaap_SharePrice
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of vested portions of options outstanding and currently exercisable.

+ References

+ Details

Name:	us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Weighted average remaining contractual term for vested portions of options outstanding and currently exercisable or convertible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

+ Details

Name:	us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableWeightedAverageRemainingContractualTerm1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (e)(1)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

+ Details

Name:	us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis=var_RangeOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis=var_RangeTwoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis=var_RangeThreeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis=var_RangeFourMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: