Investments in Affiliated Companies (Operating Results, Affiliates) (Details 5) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Operating results for all affiliated companies of GATX
Revenues	$ 334.5	$ 651.8	$ 645.5
Gains on sales of assets	43.5	57.4	21.1
Equity Method Investment, Summarized Financial Information, Net Income (Loss)	$ 108.6	$ 75.3	$ 88.5