| Document and Entity Information Document and Entity Information | Oct. 28, 2020 |
| Document and Entity Information [Abstract] | |
| Entity Central Index Key | 0000105770 |
| Document Type | 8-K |
| Document Period End Date | Oct. 28, 2020 |
| Entity Registrant Name | WEST PHARMACEUTICAL SERVICES, INC. |
| Entity Incorporation, State or Country Code | PA |
| Entity File Number | 1-8036 |
| Entity Tax Identification Number | 23-1210010 |
| Entity Address, Address Line One | 530 Herman O. West Drive, |
| Entity Address, City or Town | Exton, |
| Entity Address, State or Province | PA |
| Entity Address, Postal Zip Code | 19341-0645 |
| City Area Code | 610 |
| Local Phone Number | 594-2900 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, par value $0.25 per share |
| Trading Symbol | WST |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | false |
| Amendment Flag | false |
