Investments in Affiliated Companies (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2012	Mar. 31, 2011
Operating results for all affiliated companies of GATX
Revenues	$ 171.2	$ 173.5
Pre tax income reported by affiliates	$ 10.6	$ 49.1

The amount of revenue from sale of goods and services reduced by sales returns, allowances, and discounts reported by an equity method investment of the entity.

No definition available.

Name:	us-gaap_EquityMethodInvestmentSummarizedFinancialInformationRevenue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration