Common stock exercise price.

No definition available.

Name:	mksi_CommonStockExercisePrice
Namespace Prefix:	mksi_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

- Definition

Level of performance target achieved percentage.

+ References

No definition available.

+ Details

Name:	mksi_LevelOfPerformanceTargetAchievedPercentage
Namespace Prefix:	mksi_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Maximum percentage of payroll for purchase of stock

+ References

No definition available.

+ Details

Name:	mksi_MaximumPercentageOfPayrollForPurchaseOfStock
Namespace Prefix:	mksi_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Number Of Shares Returned For Each Share Of Common Stock

+ References

No definition available.

+ Details

Name:	mksi_NumberOfSharesReturnedForEachShareOfCommonStock
Namespace Prefix:	mksi_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of payroll deduction to compensation.

+ References

No definition available.

+ Details

Name:	mksi_PercentageOfPayrollDeductionToCompensation
Namespace Prefix:	mksi_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Share based compensation arrangement by share based payment award equity instruments other than options converted to RSU upon merger.

+ References

No definition available.

+ Details

Name:	mksi_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsConvertedToRSUUponMerger
Namespace Prefix:	mksi_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Share Based Compensation Arrangement by Share Based Payment Award Equity Instruments Other than Options Converted To RSU Upon Merger And Released

+ References

No definition available.

+ Details

Name:	mksi_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsConvertedToRsuUponMergerAndReleased
Namespace Prefix:	mksi_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Share Based Compensation Arrangement by Share Based Payment Award Equity Instruments Other than Options Converted To RSU Upon Merger Remaining To Issue

+ References

No definition available.

+ Details

Name:	mksi_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsConvertedToRsuUponMergerRemainingToIssue
Namespace Prefix:	mksi_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Share based compensation arrangement by share based payment award equity instruments other than options dividend reinvestment.

+ References

No definition available.

+ Details

Name:	mksi_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsDividendReinvestment
Namespace Prefix:	mksi_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of the balance sheet date at which grantees can acquire the shares reserved for issuance on stock options awarded under the plan during the reporting period.

+ References

No definition available.

+ Details

Name:	mksi_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodPercentageExercisePrice
Namespace Prefix:	mksi_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Share based compensation arrangement by share based payment award vesting period description.

+ References

No definition available.

+ Details

Name:	mksi_ShareBasedCompensationArrangementByShareBasedPaymentAwardVestingPeriodDescription
Namespace Prefix:	mksi_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Stock exercise price as percentage of closing market price.

+ References

No definition available.

+ Details

Name:	mksi_StockExercisePriceAsPercentageOfClosingMarketPrice
Namespace Prefix:	mksi_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of shares of equity interests issued or issuable to acquire entity.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (b)(4)
-URI http://asc.fasb.org/extlink&oid=120321790&loc=d3e6927-128479

+ Details

Name:	us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Aggregate number of common shares reserved for future issuance.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.29)
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

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

- Definition

Total number of common shares of an entity that have been sold or granted to shareholders (includes common shares that were issued, repurchased and remain in the treasury). These shares represent capital invested by the firm's shareholders and owners, and may be all or only a portion of the number of shares authorized. Shares issued include shares outstanding and shares held in the treasury.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(29))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

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

- Definition

The maximum number of shares authorized for issuance under the deferred compensation arrangement as of the balance sheet date.

+ 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 (a)(3)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

+ Details

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

- Definition

Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

+ 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 (i)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

+ Details

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

- Definition

Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents 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 (i)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

+ Details

Name:	us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target 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)(2)(iii)(1)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

+ Details

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

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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

- Definition

The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

+ 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

+ Details

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

- Definition

Percentage of vesting of award under share-based payment arrangement.

+ 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 (a)(1)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

+ Details

Name:	us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Fair value of options vested. Excludes equity instruments other than options, for example, but not limited to, share units, stock appreciation rights, restricted stock.

+ 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)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

+ Details

Name:	us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedInPeriodFairValue1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_RestrictedStockUnitsRSUMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BusinessAcquisitionAxis=mksi_NewportCorporationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VestingAxis=us-gaap_ShareBasedCompensationAwardTrancheOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=mksi_RestrictedStockUnitsGrantedToEmployeesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=mksi_RestrictedStockUnitsGrantedToDirectorsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_StockAppreciationRightsSARSMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PlanNameAxis=mksi_TwoThousandFourteenEmployeeStockPurchasePlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_PlanNameAxis=mksi_StockIncentivePlanTwoThousandFourteenMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PlanNameAxis=mksi_NewportDeferredCompensationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_TitleOfIndividualAxis=mksi_OutsideDirectorsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PlanNameAxis=mksi_EsiPlanmemberMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Stock-Based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions		1 Months Ended				12 Months Ended
	Apr. 29, 2016	May 31, 2020	Jan. 31, 2020	May 31, 2019	May 31, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock, shares issued						55,196,501	54,596,183
Common stock reserved for issuance						18,000,000
Weighted Average Grant Date Fair Value, Granted						$ 23.88	$ 16.04	$ 21.74
Restricted Stock Units (RSUs) [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares available for future grant						18,000,000
Shares issued as per merger agreement						1,260,525
Number of RSUs outstanding						4,875	5,794
Dividend reinvestment						35	57
Total intrinsic value of options, stock appreciation rights exercised and fair value of RSUs vested						$ 86.2	$ 68.1	$ 61.6
Total compensation expense related to restricted stock unites and stock appreciation rights						$ 31.5
Estimated weighted average amortization period						1 year
Restricted Stock Units (RSUs) [Member] \| Newport Corporation
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares issued as per merger agreement						360,674
Restricted Stock Units (RSUs) [Member] \| Share-based Compensation Award, Tranche One [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting percentage per year of RSUs from date of grant						33.00%	33.00%	33.00%
RSUs Granted to Employees [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share based compensation arrangement by share based payment award vesting period description						employees who meet certain retirement eligibility requirements will vest in full upon each such employee’s retirement and are expensed immediately.
RSUs Granted To Directors [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share based compensation arrangement by share based payment award vesting period description						directors generally vest at the earliest of (1) one day prior to the next annual meeting, (2) 13 months from date of grant, or (3) the effective date of a change in control of the Company.
Stock Appreciation Rights (SARs) [Member] \| Newport Corporation
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares issued as per merger agreement						899,851
2014 ESPP [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares authorized for issuance						2,500,000
Percentage of payroll deduction to compensation						up to 10%
Percentage of Common Stock through payroll deductions						10.00%
Percentage of closing price of the Common Stock						90.00%
Common stock, shares issued						102,719	126,407	105,672
Common stock reserved for issuance						1,697,604
2014 ESPP [Member] \| Offer Terminate [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of closing price of the Common Stock						90.00%
Stock Incentive Plan 2014 [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock reserved for issuance						12,690,974
Shares available for future grant						18,000,000
Number of shares returned for each common stock						2.4
Percentage of exercise price fair value option grant in period						100.00%
Stock Incentive Plan 2014 [Member] \| Restricted Stock Units (RSUs) [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted Average Grant Date Fair Value, Granted						$ 98.72
Newport Deferred Compensation [Member] \| Restricted Stock Units (RSUs) [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Number of RSUs outstanding						31,458	327,328
Dividend reinvestment						203	3,086
Newport Deferred Compensation [Member] \| Restricted Stock Units (RSUs) [Member] \| Outside Directors [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Newport RSUs converted to MKS RSUs at Merger date						36,599
Newport RSUs converted to MKS RSUs at Merger date and released		976		967	5,561
Esi Planmember \| Restricted Stock Units (RSUs) [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares issued as per merger agreement						748,920
Esi Planmember \| Restricted Stock Units (RSUs) [Member] \| Outside Directors [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Newport RSUs converted to MKS RSUs at Merger date						326,283
Newport RSUs converted to MKS RSUs at Merger date and released			300,654
Esi Planmember \| Restricted Stock Units (RSUs) [Member] \| Newport Corporation
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares issued as per merger agreement	736,133
Esi Planmember \| Stock Appreciation Rights (SARs) [Member] \| Newport Corporation
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares issued as per merger agreement	12,787
Minimum [Member] \| Restricted Stock Units (RSUs) [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Level of performance target achieved						0.00%
Minimum [Member] \| 2014 ESPP [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock, exercise price						$ 95.07	$ 64.31	$ 84.11
Maximum [Member] \| Restricted Stock Units (RSUs) [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Level of performance target achieved						150.00%
Maximum [Member] \| 2014 ESPP [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock, exercise price						$ 93.77	$ 63.78	$ 70.61