Debt (Details Textual) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) Instrument	Dec. 31, 2016 USD ($) Instrument	Dec. 31, 2015 USD ($)
Line of Credit Facility [Line Items]
Operating assets pledged as collateral for notes	$ 319.1
Other Short-term Borrowings	4.3	$ 3.8
Annual commitment fees	$ 2.0	$ 1.5	$ 1.0
Fixed charge coverage ratio	2.4
Minimum debt covenant fixed charge coverage ratio	1.2
Amount of secured debt available to be borrowed in accordance with public debt covenants	$ 1,415.5
Line of Credit US [Member]
Line of Credit Facility [Line Items]
Unsecured revolving credit facility	600.0
Rail Facility [Member]
Line of Credit Facility [Line Items]
Unsecured revolving credit facility	250.0
Line of Credit Europe [Member]
Line of Credit Facility [Line Items]
Maximum amount of GRE transfer to GATX relating to loans and dividends	259.1
Restricted net assets	$ 398.3
Fair Value Hedging [Member]
Line of Credit Facility [Line Items]
Derivative, Number of Instruments Held | Instrument	10	8
Rail Facility [Member]
Line of Credit Facility [Line Items]
Unsecured revolving credit facility	$ 250.0