Description of Business	6 Months Ended
Jun. 30, 2026
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 January 1, 2026, GATX acquired approximately 101,000 railcars for $4.2 billion from Wells Fargo Bank, N.A. ("Wells Fargo") through a newly formed joint venture ("GABX" or the "GABX joint venture") with Brookfield Infrastructure Partners L.P. and its institutional partners (collectively, "Brookfield"). Initially, GATX's ownership share of GABX was 30% with Brookfield's share at 70%. The acquisition from Wells Fargo was funded through a $2.96 billion term loan executed by GABX, which is guaranteed by GATX Corporation, and equity contributions of $385.3 million from GATX and $899.0 million from Brookfield. As of June 30, 2026, GABX is a consolidated variable interest entity and is reported in the Rail North America segment. See "Note 3. Asset Acquisition" and "Note 7. Variable Interest Entities" for further information about the transaction and GABX consolidation. Also on January 1, 2026, GATX directly purchased 200 locomotives from Wells Fargo for approximately $30.4 million, and Brookfield directly acquired Wells Fargo’s rail finance lease portfolio, consisting of approximately 22,000 railcars and approximately 400 locomotives. GATX serves as manager of the railcars in GABX as well as the finance lease portfolio directly owned by Brookfield and earns management fees for such services. GATX has the option to acquire up to 100% of the ownership of GABX over time. On June 30, 2026, GATX exercised its first call option for $66.2 million, resulting in GATX increasing its overall ownership of GABX from 30% to 33.5% and Brookfield's overall ownership reducing from 70% to 66.5%. See "Note 15. Non-Controlling Interest" for further information about the options to increase GATX's ownership of GABX.

Description of Business

6 Months Ended

Jun. 30, 2026

Organization, Consolidation and Presentation of Financial Statements [Abstract]

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 January 1, 2026, GATX acquired approximately 101,000 railcars for $4.2 billion from Wells Fargo Bank, N.A. ("Wells Fargo") through a newly formed joint venture ("GABX" or the "GABX joint venture") with Brookfield Infrastructure Partners L.P. and its institutional partners (collectively, "Brookfield"). Initially, GATX's ownership share of GABX was 30% with Brookfield's share at 70%. The acquisition from Wells Fargo was funded through a $2.96 billion term loan executed by GABX, which is guaranteed by GATX Corporation, and equity contributions of $385.3 million from GATX and $899.0 million from Brookfield. As of June 30, 2026, GABX is a consolidated variable interest entity and is reported in the Rail North America segment. See "Note 3. Asset Acquisition" and "Note 7. Variable Interest Entities" for further information about the transaction and GABX consolidation.

Also on January 1, 2026, GATX directly purchased 200 locomotives from Wells Fargo for approximately $30.4 million, and Brookfield directly acquired Wells Fargo’s rail finance lease portfolio, consisting of approximately 22,000 railcars and approximately 400 locomotives. GATX serves as manager of the railcars in GABX as well as the finance lease portfolio directly owned by Brookfield and earns management fees for such services.

GATX has the option to acquire up to 100% of the ownership of GABX over time. On June 30, 2026, GATX exercised its first call option for $66.2 million, resulting in GATX increasing its overall ownership of GABX from 30% to 33.5% and Brookfield's overall ownership reducing from 70% to 66.5%. See "Note 15. Non-Controlling Interest" for further information about the options to increase GATX's ownership of GABX.