CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Parenthetical) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Statement of Comprehensive Income [Abstract]
Foreign currency translation adjustments, tax	$ 3.6	$ 1.0	$ 2.2
Net actuarial gain (loss) arising during period, tax	0.3	0.4	(2.4)
Settlement effects arising during period, tax	0.0	0.0	20.3
Amortization of actuarial (gain) loss, tax	(0.2)	(0.4)	(0.1)
Amortization of other, tax	0.0	(0.1)	0.1
Net gain (loss) on equity affiliate accumulated other comprehensive income, tax	0.0	0.0	0.0
Net (loss) gain on derivatives, tax	$ (0.9)	$ 0.0	$ 0.2

Amount of tax expense (benefit) allocated to other comprehensive income (loss) (OCI) for proportionate share of equity method investee's OCI, attributable to parent.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 323
-SubTopic 10
-Name Accounting Standards Codification
-Section 35
-Paragraph 18
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481725/323-10-35-18

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 810
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1A
-Subparagraph (c)(3)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481203/810-10-50-1A

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 810
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 19
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481231/810-10-45-19

+ Details

Name:	us-gaap_OciEquityMethodInvestmentTaxParent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of tax expense (benefit) for (increase) decrease in value of benefit obligation for change in actuarial assumptions and increase (decrease) in value of plan assets from experience different from that assumed of defined benefit plan, that has not been recognized in net periodic benefit (cost) credit.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 45
-Paragraph 12
-SubTopic 10
-Topic 220
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482790/220-10-45-12

+ Details

Name:	us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansNetUnamortizedGainLossArisingDuringPeriodTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of tax expense (benefit), after reclassification adjustments of gain (loss) on foreign currency translation adjustments, foreign currency transactions designated and effective as economic hedges of a net investment in a foreign entity and intra-entity foreign currency transactions that are of a long-term-investment nature, attributable to parent entity.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 810
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 19
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481231/810-10-45-19

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 45
-Paragraph 20
-SubTopic 10
-Topic 810
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481231/810-10-45-20

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 1A
-Subparagraph (c)(3)
-SubTopic 10
-Topic 810
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481203/810-10-50-1A

+ Details

Name:	us-gaap_OtherComprehensiveIncomeForeignCurrencyTranslationAdjustmentTaxPortionAttributableToParent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of tax expense (benefit) for adjustments from accumulated other comprehensive income (AOCI) for gain (loss) from increase (decrease) in value of excluded component of derivative designated and qualifying as hedge. Adjustments include, but are not limited to, reclassifications for sale and settlement, and amounts recognized under systematic and rational method.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 11
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482790/220-10-45-11

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 15
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482790/220-10-45-15

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 10A
-Subparagraph (dd)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482790/220-10-45-10A

+ Details

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

- Definition

Amount of tax expense (benefit) of reclassification adjustment from accumulated other comprehensive income (loss) for gain (loss) of defined benefit plan.

+ References

+ Details

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

- Definition

Amount of tax expense (benefit) for reclassification adjustment from accumulated other comprehensive income (loss) for transition asset (obligation) of defined benefit plan.

+ References

+ Details

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

- References

No definition available.

+ Details

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

- Definition

Other Comprehensive Income (Loss), Defined Benefit Plans, Settlement Effects Arising During Period, Tax

+ References

No definition available.

+ Details

Name:	wst_OtherComprehensiveIncomeLossDefinedBenefitPlansSettlementEffectsArisingDuringPeriodTax
Namespace Prefix:	wst_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration