Segment Information - Financial information for segments (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Segment Reporting Information [Line Items]
External Revenue	$ 736.0	$ 634.0	$ 1,340.8	$ 1,167.2
Total revenues	736.0	634.0	1,340.8	1,167.2
Operating Profit (Loss)	107.0	88.0	198.8	150.1
Intersegment
Segment Reporting Information [Line Items]
Intersegment Revenues	0.0	0.0	0.0	0.0
Intersegment | Eliminations – Lease subsidiary
Segment Reporting Information [Line Items]
Intersegment Revenues	(328.9)	(228.5)	(599.0)	(524.6)
Total revenues	(328.9)	(228.5)	(599.0)	(524.6)
Operating Profit (Loss)	(41.6)	(24.5)	(68.8)	(53.2)
Intersegment | Eliminations – Other
Segment Reporting Information [Line Items]
Intersegment Revenues	(13.0)	(9.3)	(28.5)	(20.0)
Total revenues	(13.0)	(9.3)	(28.5)	(20.0)
Operating Profit (Loss)	0.2	(0.3)	(0.2)	(0.2)
Total
Segment Reporting Information [Line Items]
Total revenues	736.0	634.0	1,340.8	1,167.2
Rail Group
Segment Reporting Information [Line Items]
External Revenue	383.4	337.7	716.9	629.7
Rail Group | Intersegment
Segment Reporting Information [Line Items]
Intersegment Revenues	328.9	228.5	599.0	524.6
Rail Group | Total
Segment Reporting Information [Line Items]
Total revenues	712.3	566.2	1,315.9	1,154.3
Operating Profit (Loss)	68.0	48.5	118.6	100.0
Railcar Leasing and Management Services Group
Segment Reporting Information [Line Items]
External Revenue	276.9	213.2	477.1	387.5
Railcar Leasing and Management Services Group | Intersegment
Segment Reporting Information [Line Items]
Intersegment Revenues	0.2	0.2	0.4	0.5
Railcar Leasing and Management Services Group | Total
Segment Reporting Information [Line Items]
Total revenues	277.1	213.4	477.5	388.0
Operating Profit (Loss)	104.8	91.8	190.6	162.9
All Other
Segment Reporting Information [Line Items]
External Revenue	75.7	83.1	146.8	150.0
All Other | Intersegment
Segment Reporting Information [Line Items]
Intersegment Revenues	12.8	9.1	28.1	19.5
All Other | Total
Segment Reporting Information [Line Items]
Total revenues	88.5	92.2	174.9	169.5
Operating Profit (Loss)	6.2	12.4	12.8	18.2
Corporate | Total
Segment Reporting Information [Line Items]
Total revenues	0.0	0.0	0.0	0.0
Operating Profit (Loss)	$ (30.6)	$ (39.9)	$ (54.2)	$ (77.6)