v3.26.1
GATX Corporation Master Trust - Schedule of Master Trust Net Assets (Details) - EBP 002 - USD ($)
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Plus:      
Net assets available for benefits $ 266,109,338 $ 240,350,870 $ 213,604,227
Master Trust Balances      
EBP, Master Trust [Line Items]      
Total investments at fair value 287,555,524 260,354,885  
Plus:      
Other receivables 918 1,195  
Net assets available for benefits 287,556,442 260,356,080  
Master Trust Balances | Mutual funds      
EBP, Master Trust [Line Items]      
Total investments at fair value 114,161,653 98,986,627  
Master Trust Balances | GATX common stock fund      
EBP, Master Trust [Line Items]      
Total investments at fair value 31,944,636 30,869,976  
Master Trust Balances | Collective trusts      
EBP, Master Trust [Line Items]      
Total investments at fair value 141,449,235 130,498,282  
Plan's Interest in Master Trust Balances      
EBP, Master Trust [Line Items]      
Total investments at fair value 263,755,309 238,225,424  
Plus:      
Other receivables 891 1,147  
Net assets available for benefits 263,756,200 238,226,571  
Plan's Interest in Master Trust Balances | Mutual funds      
EBP, Master Trust [Line Items]      
Total investments at fair value 97,117,908 84,186,812  
Plan's Interest in Master Trust Balances | GATX common stock fund      
EBP, Master Trust [Line Items]      
Total investments at fair value 30,995,772 29,640,088  
Plan's Interest in Master Trust Balances | Collective trusts      
EBP, Master Trust [Line Items]      
Total investments at fair value $ 135,641,629 $ 124,398,524