v3.10.0.1
Document and Entity Information - USD ($)
12 Months Ended
Dec. 31, 2018
Jan. 31, 2019
Jun. 30, 2018
Document and Entity Information [Abstract]      
Entity Registrant Name WEST PHARMACEUTICAL SERVICES INC    
Entity Central Index Key 0000105770    
Document Type 10-K    
Document Period End Date Dec. 31, 2018    
Current Fiscal Year End Date --12-31    
Document Fiscal Year Focus 2018    
Document Fiscal Period Focus FY    
Amendment Flag false    
Entity Well-known Seasoned Issuer Yes    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Filer Category Large Accelerated Filer    
Entity Small Business false    
Entity Emerging Growth Company false    
Entity Shell Company false    
Entity Public Float     $ 7,301,615,623
Entity Common Stock, Shares Outstanding   74,186,169