Leases Lessee, Schedule of Finance Leases (Details) $ in Millions	12 Months Ended
Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($) tankContainer	Dec. 31, 2021 USD ($) tankContainer
Lessee, Lease, Description [Line Items]
Number of railcars received \| tankContainer		21	2,329
gatxOperatingLeaseOtherIncome \| $	$ 94.6	$ 81.5	$ 74.8

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 842
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147478964/842-20-50-3

Name:	us-gaap_LesseeLeaseDescriptionLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration