Leases (Details 3) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011
Capital Leases
2013, Capital Leases	$ 3.1
2014, Capital Leases	3.1
2015, Capital Leases	3.1
2016, Capital Leases	2.7
2017, Capital Leases	1.1
Years thereafter, Capital Leases	0
Capital Leases, Future Minimum Payments Due, Total	13.1
Less: amounts representing interest	(1.8)
Present value of future minimum capital lease payments	11.3		14.3
Recourse Operating Leases [Member]
Operating Leases
2013, Operating Lease	115.3	[1]
2014, Operating Lease	119.7	[1]
2015, Operating Lease	139.7	[1]
2016, Operating Lease	101.5	[1]
2017, Operating Lease	89.3	[1]
Years thereafter, Operating Leases	417.4	[1]
Total, Operating Leases	982.9	[1]
Nonrecourse Operating Leases [Member]
Operating Leases
2013, Operating Lease	27.9	[2]
2014, Operating Lease	27.4	[2]
2015, Operating Lease	26.0	[2]
2016, Operating Lease	21.9	[2]
2017, Operating Lease	22.5	[2]
Years thereafter, Operating Leases	75.3	[2]
Total, Operating Leases	$ 201.0	[2]

[1] The contractual rental payments do not include the costs of licenses, taxes, insurance, and maintenance, for which GATX is required to pay.

[2] The amounts shown for nonrecourse operating leases primarily reflect the rental payments of two wholly-owned bankruptcy-remote, SPCs. These rentals are consolidated for accounting purposes, but do not represent legal obligations of GATX.