Segment Information - Financial information for segments (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2022	Mar. 31, 2022	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2022	Jun. 30, 2021
Segment Reporting Information [Line Items]
External Revenue	$ 416.8		$ 293.3		$ 889.5	$ 624.0
Revenues, Total	416.8		293.3		889.5	624.0
Operating Profit (Loss)	73.0		57.8		127.8	109.3
Restructuring activities, net	(1.0)		0.7		(1.0)	1.0
Other (income) expense	50.7		63.5		92.6	116.0
Provision (benefit) for income taxes	5.8		(2.9)		8.8	1.1
Income (loss) from discontinued operations, net of provision (benefit) for income taxes of $(0.5), $2.1, $(2.5), and $4.4	(3.4)		7.6		(10.3)	13.9
Loss on sale of discontinued operations, net of benefit for income taxes of $1.0, $—, $1.4, and $—	(4.6)		0.0		(5.7)	0.0
Net income	8.5	$ 1.9	4.8	$ 1.3	10.4	6.1
Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues, Total	416.8		293.3		889.5	624.0
Operating Profit (Loss)	119.2		84.3		199.8	153.8
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment Revenues					0.0	0.0
Intersegment Eliminations [Member] | Consolidated Subsidiaries, Leasing [Member]
Segment Reporting Information [Line Items]
External Revenue					0.0	0.0
Intersegment Revenues	(208.9)		(151.0)		(310.2)	(262.3)
Revenues, Total	(208.9)		(151.0)		(310.2)	(262.3)
Operating Profit (Loss)	(20.3)		(3.0)		(29.1)	(4.8)
Intersegment Eliminations [Member] | Consolidated Subsidiaries, Excluding Leasing [Member]
Segment Reporting Information [Line Items]
External Revenue					0.0	0.0
Intersegment Revenues	(0.2)		(2.6)		(0.4)	(5.1)
Revenues, Total	(0.2)		(2.6)		(0.4)	(5.1)
Operating Profit (Loss)	0.2		(0.3)		(1.1)	(0.7)
Railcar Leasing and Management Services Group [Member]
Segment Reporting Information [Line Items]
External Revenue	195.1		185.0		378.0	368.3
Railcar Leasing and Management Services Group [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues, Total	195.3		185.1		378.4	368.6
Operating Profit (Loss)	105.5		81.1		185.3	159.4
Railcar Leasing and Management Services Group [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment Revenues	0.2		0.1		0.4	0.3
Rail Products Group [Member]
Segment Reporting Information [Line Items]
External Revenue	221.7		108.3		511.5	255.7
Rail Products Group [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues, Total	430.6		261.8		821.7	522.8
Operating Profit (Loss)	13.7		3.2		14.5	(5.6)
Rail Products Group [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment Revenues	208.9		153.5		310.2	267.1
Corporate Segment [Member]
Segment Reporting Information [Line Items]
Operating Profit (Loss)	$ (25.1)		$ (23.9)		$ (40.8)	$ (40.0)