Segment Information - Financial information for segments (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Segment Reporting Information [Line Items]
External Revenue	$ 813.6	$ 606.9	$ 2,154.4	$ 1,774.1
Total revenues	813.6	606.9	2,154.4	1,774.1
Operating Profit (Loss)	120.3	75.2	319.1	225.3
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	(314.0)	(207.4)	(913.0)	(732.0)
Total revenues	(314.0)	(207.4)	(913.0)	(732.0)
Operating Profit (Loss)	(40.7)	(18.1)	(109.5)	(71.3)
Intersegment | Eliminations – Other
Segment Reporting Information [Line Items]
Intersegment Revenues	(12.2)	(13.2)	(40.7)	(33.2)
Total revenues	(12.2)	(13.2)	(40.7)	(33.2)
Operating Profit (Loss)	(0.1)	1.0	(0.3)	0.8
Total
Segment Reporting Information [Line Items]
Total revenues	813.6	606.9	2,154.4	1,774.1
Rail Group
Segment Reporting Information [Line Items]
External Revenue	409.0	290.2	1,125.9	919.9
Rail Group | Intersegment
Segment Reporting Information [Line Items]
Intersegment Revenues	314.0	207.4	913.0	732.0
Rail Group | Total
Segment Reporting Information [Line Items]
Total revenues	723.0	497.6	2,038.9	1,651.9
Operating Profit (Loss)	65.4	28.0	184.0	128.0
Railcar Leasing and Management Services Group
Segment Reporting Information [Line Items]
External Revenue	326.2	227.2	803.3	614.7
Railcar Leasing and Management Services Group | Intersegment
Segment Reporting Information [Line Items]
Intersegment Revenues	0.2	0.3	0.6	0.8
Railcar Leasing and Management Services Group | Total
Segment Reporting Information [Line Items]
Total revenues	326.4	227.5	803.9	615.5
Operating Profit (Loss)	115.7	92.2	306.3	255.1
All Other
Segment Reporting Information [Line Items]
External Revenue	78.4	89.5	225.2	239.5
All Other | Intersegment
Segment Reporting Information [Line Items]
Intersegment Revenues	12.0	12.9	40.1	32.4
All Other | Total
Segment Reporting Information [Line Items]
Total revenues	90.4	102.4	265.3	271.9
Operating Profit (Loss)	3.9	9.5	16.7	27.7
Corporate | Total
Segment Reporting Information [Line Items]
Total revenues	0.0	0.0	0.0	0.0
Operating Profit (Loss)	$ (23.9)	$ (37.4)	$ (78.1)	$ (115.0)