Legal Proceedings and Other Contingencies	3 Months Ended
	Mar. 31, 2021
Commitments and Contingencies Disclosure [Abstract]
Legal Proceedings and Other Contingencies	Legal Proceedings and Other Contingencies Various legal actions, claims, assessments and other contingencies arising in the ordinary course of business are pending against GATX and certain of our subsidiaries. These matters are subject to many uncertainties, and it is possible that some of these matters could ultimately be decided, resolved or settled adversely. For a full discussion of our pending legal matters, please refer to the notes included with our consolidated financial statements in our Annual Report on Form 10-K for the year ended December 31, 2020.