Investments in Affiliated Companies (Textual) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2023 USD ($) Business_Activity AircraftEngines	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Schedule of Equity Method Investments [Line Items]
Asset Impairment Charges	$ 1.5	$ 48.9	$ 2.4
Share of affiliates' earnings (net of tax)	72.4	33.6	1.2
Portfolio proceeds	$ 272.8	269.6	187.1
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	399
Share of affiliates' earnings (net of tax)	$ 72.8	33.2	1.2
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	200
RRPF Joint Ventures [Member] | Minimum [Member]
Schedule of Equity Method Investments [Line Items]
Lease term	3 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	$ 1.2	$ 34.3	$ 0.0