Description of Business	6 Months Ended
Jun. 30, 2025
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Description of Business	Description of Business As used herein, "GATX," "we," "us," "our," and similar terms refer to GATX Corporation and its subsidiaries, unless indicated otherwise. We lease, operate, manage, and remarket long-lived, widely used assets, primarily in the rail market. We report our financial results through three primary business segments: Rail North America, Rail International, and Engine Leasing. Financial results for our tank container leasing business ("Trifleet") are reported in the Other segment. On May 29, 2025 GATX entered into a definitive agreement to acquire approximately 105,000 railcars from Wells Fargo Bank, N.A. ("Wells Fargo") for $4.4 billion through a newly formed joint venture with Brookfield Infrastructure Partners L.P. and its institutional partners (collectively, “Brookfield”). Initially, GATX's ownership share in the joint venture will be 30%, with Brookfield's share at 70%. GATX will have the option to acquire up to 100% of the joint venture equity over time. A portion of the purchase price will be financed by the joint venture in the form of debt financing. GATX will guarantee the joint venture’s debt financing obligations. In the second quarter of 2025, the newly formed joint venture entered into deal contingent interest rate swaps, with total notional value of $2.4 billion, in order to hedge the exposure on the debt financing expected upon closing of the transaction. The hedges are designated as cash flow hedges. GATX will also directly purchase approximately 223 locomotives from Wells Fargo, and Brookfield will directly acquire Wells Fargo’s rail finance lease portfolio. GATX will serve as manager of the railcars in the joint venture as well as the finance lease portfolio directly owned by Brookfield. The transaction is subject to customary closing conditions, including required regulatory approvals and clearances, and is expected to close in the first quarter of 2026 or sooner.

We lease, operate, manage, and remarket long-lived, widely used assets, primarily in the rail market. We report our financial results through three primary business segments: Rail North America, Rail International, and Engine Leasing. Financial results for our tank container leasing business ("Trifleet") are reported in the Other segment.

On May 29, 2025 GATX entered into a definitive agreement to acquire approximately 105,000 railcars from Wells Fargo Bank, N.A. ("Wells Fargo") for $4.4 billion through a newly formed joint venture with Brookfield Infrastructure Partners L.P. and its institutional partners (collectively, “Brookfield”). Initially, GATX's ownership share in the joint venture will be 30%, with Brookfield's share at 70%. GATX will have the option to acquire up to 100% of the joint venture equity over time. A portion of the purchase price will be financed by the joint venture in the form of debt financing. GATX will guarantee the joint venture’s debt financing obligations. In the second quarter of 2025, the newly formed joint venture entered into deal contingent interest rate swaps, with total notional value of $2.4 billion, in order to hedge the exposure on the debt financing expected upon closing of the transaction. The hedges are designated as cash flow hedges. GATX will also directly purchase approximately 223 locomotives from Wells Fargo, and Brookfield will directly acquire Wells Fargo’s rail finance lease portfolio. GATX will serve as manager of the railcars in the joint venture as well as the finance lease portfolio directly owned by Brookfield. The transaction is subject to customary closing conditions, including required regulatory approvals and clearances, and is expected to close in the first quarter of 2026 or sooner.