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Document and Entity Information Statement
Nov. 12, 2020
Nov. 06, 2020
Document Information [Line Items]    
Document Type 8-K  
Document Period End Date Nov. 12, 2020  
Entity Registrant Name GATX Corporation  
Entity Incorporation, State or Country Code NY  
Entity File Number 1-2328  
Entity Tax Identification Number 36-1124040  
Entity Address, Address Line One 233 South Wacker Drive  
Entity Address, City or Town Chicago  
Entity Address, State or Province IL  
Entity Address, Postal Zip Code 60606  
City Area Code 312  
Local Phone Number 621-6200  
Written Communications false  
Soliciting Material false  
Pre-commencement Tender Offer false  
Pre-commencement Issuer Tender Offer false  
Entity Emerging Growth Company false  
Amendment Flag   false
Entity Central Index Key   0000040211
CHICAGO STOCK EXCHANGE, INC [Member]    
Document Information [Line Items]    
Security Exchange Name CHX  
Common Stock [Member] | NEW YORK STOCK EXCHANGE, INC. [Member]    
Document Information [Line Items]    
Title of 12(b) Security Common Stock  
Trading Symbol GATX  
Security Exchange Name NYSE  
Senior Notes [Member] | NEW YORK STOCK EXCHANGE, INC. [Member]    
Document Information [Line Items]    
Title of 12(b) Security 5.625% Senior Notes due 2066  
Trading Symbol GMTA  
Security Exchange Name NYSE