Investments in Affiliated Companies (Textual) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2024 USD ($) AircraftEngines Business_Activity	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)
Schedule of Equity Method Investments [Line Items]
Asset Impairment Charges	$ 0.0	$ 1.5	$ 48.9
Share of affiliates' earnings (net of tax)	82.8	72.4	33.6
Portfolio proceeds	$ 230.6	272.8	269.6
RRPF Joint Ventures [Member]
Schedule of Equity Method Investments [Line Items]
GATX ownership percentage in joint venture	50.00%
Number of business activities | Business_Activity	2
Number of Aircraft Engines Under Leasing Arrangement | AircraftEngines	427
Share of affiliates' earnings (net of tax)	$ 82.8	72.8	33.2
RRPF Joint Ventures [Member] | Russia
Schedule of Equity Method Investments [Line Items]
Asset Impairment Charges			11.5
RRPF Joint Ventures [Member] | Rolls-Royce [Member]
Schedule of Equity Method Investments [Line Items]
Number of Aircraft Engines Under Leasing Arrangement | AircraftEngines	198
RRPF Joint Ventures [Member] | Minimum [Member]
Schedule of Equity Method Investments [Line Items]
Lease term	5 years
RRPF Joint Ventures [Member] | Maximum [Member]
Schedule of Equity Method Investments [Line Items]
Lease term	12 years
RRPF Joint Ventures [Member] | Aircraft Engines [Member] | Minimum [Member]
Schedule of Equity Method Investments [Line Items]
Estimated useful lives of depreciable assets	20 years
RRPF Joint Ventures [Member] | Aircraft Engines [Member] | Maximum [Member]
Schedule of Equity Method Investments [Line Items]
Estimated useful lives of depreciable assets	30 years
Portfolio Management [Member]
Schedule of Equity Method Investments [Line Items]
Asset Impairment Charges	$ 0.0	$ 1.2	$ 34.3