Fair Value Disclosure (Details 2) (USD $) In Millions	3 Months Ended	9 Months Ended
Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Impact of GATX's Derivative Instrument on Income Statement and Other comprehensive income (loss)
Interest expense	$ 0.4	$ 4.0	$ (0.3)	$ 11.7
Amount recognized in other comprehensive income (loss) (effective portion)	0.8	(2.7)	(5.1)	(10.9)
Amount recognized in other expense (ineffective portion)	(0.4)		(0.4)	(0.1)
Interest Expense [Member] \| Cash Flow Hedging [Member]
Impact of GATX's Derivative Instrument on Income Statement and Other comprehensive income (loss)
Amount reclassified from accumulated other comprehensive loss	(2.1)	(2.0)	(6.0)	(5.7)
Operating Lease Expense [Member] \| Cash Flow Hedging [Member]
Impact of GATX's Derivative Instrument on Income Statement and Other comprehensive income (loss)
Amount reclassified from accumulated other comprehensive loss	$ (0.4)	$ (0.4)	$ (1.2)	$ (1.2)

The amount recognized in earnings related to the change in fair value during the period of derivative or nonderivative instruments designated as fair value hedging instruments.

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The effective portion of net gain (loss) reclassified from accumulated other comprehensive income into income on derivative instruments designated and qualifying as hedging instruments.

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