Investments in Affiliated Companies (Future Lease Receipts) (Details 8) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012
Schedule of Equity Method Investments [Line Items]
2013	$ 784.4	[1]
2014	594.2	[1]
2015	465.8	[1]
2016	346.1	[1]
2017	223.0	[1]
Years thereafter	461.7	[1]
Total future receipts from leases	2,875.2	[1]
RRPF Joint Ventures [Member]
Schedule of Equity Method Investments [Line Items]
2013	254.0
2014	233.5
2015	219.4
2016	199.9
2017	169.4
Years thereafter	457.1
Total future receipts from leases	1,533.3
RRPF Joint Ventures [Member] | Rolls-Royce [Member]
Schedule of Equity Method Investments [Line Items]
2013	120.9
2014	118.9
2015	119.7
2016	111.3
2017	89.4
Years thereafter	275.0
Total future receipts from leases	835.2
RRPF Joint Ventures [Member] | Third Parties [Member]
Schedule of Equity Method Investments [Line Items]
2013	133.1
2014	114.6
2015	99.7
2016	88.6
2017	80.0
Years thereafter	182.1
Total future receipts from leases	$ 698.1

[1] The future contractual receipts due under operating leases include executory costs in the case of GATX's full service leases.