Railcar Leasing and Management Services Group - Schedule of proceeds from leased railcars (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Property Subject to or Available for Operating Lease [Line Items]
Proceeds from sale leased railcars	$ 85.6	$ 99.5
Railcar Leasing and Management Services Group | Railcars owned one year or less at the time of sale
Property Subject to or Available for Operating Lease [Line Items]
Proceeds from sale leased railcars	29.2	7.1
Railcar Leasing and Management Services Group | Railcars owned more than one year at the time of sale
Property Subject to or Available for Operating Lease [Line Items]
Proceeds from sale leased railcars	56.4	92.4
Rail Group
Property Subject to or Available for Operating Lease [Line Items]
Proceeds from sale leased railcars	$ 0.0	$ 0.0