v3.26.1
Cover - shares
6 Months Ended
Jun. 30, 2026
Jul. 24, 2026
Cover [Abstract]    
Document Type 10-Q  
Document Quarterly Report true  
Document Period End Date Jun. 30, 2026  
Document Transition Report false  
Entity File Number 001-42161  
Registrant Name Smurfit Westrock plc  
Entity Incorporation, State or Country Code L2  
Entity Tax Identification Number 98-1776979  
Entity Address, Address Line One Beech Hill, Clonskeagh,  
Entity Address, City or Town Dublin 4  
Entity Address, Postal Zip Code D04 N2R2  
Entity Address, Country IE  
City Area Code +353  
Local Phone Number 1 202 7000  
Title of 12(b) Security Ordinary shares, par value $0.001 per share  
Trading Symbol SW  
Security Exchange Name NYSE  
Entity Current Reporting Status Yes  
Entity Interactive Data Current Yes  
Entity Filer Category Large Accelerated Filer  
Entity Small Business false  
Entity Emerging Growth Company false  
Entity Shell Company false  
Entity Common Stock, Shares Outstanding   524,522,908
Entity Central Index Key 0002005951  
Current Fiscal Year End Date --12-31  
Document Fiscal Year Focus 2026  
Document Fiscal Period Focus (i.e. Q1,Q2,Q3,FY) Q2  
Amendment Flag false