Debt (Details 1) - USD ($)	Dec. 31, 2025	Dec. 31, 2024
Debt Disclosure [Abstract]
Weighted-average interest rate	4.78%	4.59%
Weighted-average term, in years	$ 8.2	$ 8.6
Maturities of GATX's debt obligations
2026	653,300,000
2027	854,500,000
2028	824,800,000
2029	907,400,000
2030	3,660,400,000
Thereafter	5,605,200,000
Total debt principal	12,505,600,000	8,270,900,000
Balance	$ 82,200,000	$ 10,400,000