Debt (Details 1) - USD ($)	Dec. 31, 2023	Dec. 31, 2022
Debt Disclosure [Abstract]
Weighted-average interest rate	4.08%	3.72%
Weighted-average term, in years	$ 8.4	$ 8.6
Maturities of GATX's debt obligations
2016	526,300,000
2017	520,800,000
2018	611,900,000
2019	458,400,000
2020	735,000,000.0
Thereafter	4,598,200,000
Total debt principal	7,450,600,000	6,492,200,000
Balance	$ 11,000,000.0	$ 17,300,000