Investments in Affiliated Companies (Textual) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011 Vessel	Dec. 31, 2010
Schedule of Equity Method Investments [Line Items]
Loans to affiliated companies	$ 51.3	$ 57.7
Asset Impairment Charges	5.0	6.8	8.3
Impairment loss		5.2
GATX ownership percentage in joint venture		45.00%
Contribution for payment of outstanding debt on dissolution		62.1
Number of vessels containing liquidating distributions		6
Fair value of vessels received on dissolution		88.8
Share of affiliates' earnings (net of tax)	19.6	32.4	28.5
RRPF Joint Ventures [Member]
Schedule of Equity Method Investments [Line Items]
GATX ownership percentage in joint venture	50.00%
Number of joint venture investments	14
Number of business activities	2
Share of affiliates' earnings (net of tax)	36.7	30.8	25.4
RRPF Joint Ventures [Member] | Minimum [Member]
Schedule of Equity Method Investments [Line Items]
Lease term	7 years
RRPF Joint Ventures [Member] | Maximum [Member]
Schedule of Equity Method Investments [Line Items]
Lease term	10 years
RRPF Joint Ventures [Member] | Aircraft Engines [Member]
Schedule of Equity Method Investments [Line Items]
Estimated useful lives of depreciable assets	25 years
Fair Value, Measurements, Nonrecurring [Member] | Investments Impairment Charge [Member] | Fair Value, Inputs, Level 3 [Member] | Equity Method Investments [Member]
Schedule of Equity Method Investments [Line Items]
Asset Impairment Charges	$ 14.8