Segment Information - Financial information for segments (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020
Segment Reporting Information [Line Items]
External Revenue	$ 371.5		$ 509.2		$ 770.3	$ 1,124.4
Total Revenues	371.5		509.2		770.3	1,124.4
Operating Profit (Loss)	67.4		(307.3)		127.6	(234.3)
Impairment of long-lived assets	0.0		(369.4)		0.0	(369.4)
Restructuring activities, net	0.7		(0.3)		1.0	(5.8)
Other (income) expense	63.5		52.3		116.0	110.4
Provision (benefit) for income taxes	(0.9)		(71.8)		5.1	(219.4)
Loss from discontinued operations, net of provision (benefit) for income taxes of $—, $—, $0.4, and $(0.1)	0.0		0.0		(0.4)	(0.2)
Net income (loss)	4.8	$ 1.3	(287.8)	$ 162.3	6.1	(125.5)
Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	371.5		509.2		770.3	1,124.4
Operating Profit (Loss)	97.1		98.1		181.9	225.4
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue	0.0		0.0		0.0	0.0
Intersegment Eliminations [Member] | Consolidated Subsidiaries, Leasing [Member]
Segment Reporting Information [Line Items]
External Revenue	0.0		0.0		0.0	0.0
Intersegment Revenue	(151.0)		(156.0)		(262.3)	(346.4)
Total Revenues	(151.0)		(156.0)		(262.3)	(346.4)
Operating Profit (Loss)	(3.0)		(11.0)		(4.8)	(30.9)
Intersegment Eliminations [Member] | Consolidated Subsidiaries, Excluding Leasing [Member]
Segment Reporting Information [Line Items]
External Revenue	0.0		0.0		0.0	0.0
Intersegment Revenue	(2.6)		(2.5)		(5.1)	(6.0)
Total Revenues	(2.6)		(2.5)		(5.1)	(6.0)
Operating Profit (Loss)	(0.3)		(0.5)		(0.7)	(1.3)
Railcar Leasing and Management Services Group [Member]
Segment Reporting Information [Line Items]
External Revenue	185.0		192.6		368.3	428.7
Operating Profit (Loss)					159.4	175.8
Restructuring activities, net					0.0	0.0
Railcar Leasing and Management Services Group [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	185.1		192.8		368.6	429.1
Operating Profit (Loss)	81.1		82.9		159.4	175.8
Railcar Leasing and Management Services Group [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue	0.1		0.2		0.3	0.4
Rail Products Group [Member]
Segment Reporting Information [Line Items]
External Revenue	108.3		247.3		255.7	564.5
Operating Profit (Loss)					(5.6)	33.0
Restructuring activities, net					(0.3)	(2.6)
Rail Products Group [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	261.8		405.6		522.8	915.0
Operating Profit (Loss)	3.2		7.9
Rail Products Group [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue	153.5		158.3		267.1	350.5
All Other
Segment Reporting Information [Line Items]
External Revenue	78.2		69.3		146.3	131.2
Operating Profit (Loss)					28.1	16.6
Restructuring activities, net					1.4	3.4
All Other | Operating Segments [Member]
Segment Reporting Information [Line Items]
Total Revenues	78.2		69.3		146.3	132.7
Operating Profit (Loss)	12.8		7.3
All Other | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment Revenue	0.0		0.0		0.0	1.5
Corporate Segment [Member]
Segment Reporting Information [Line Items]
Operating Profit (Loss)	$ (27.1)		$ (24.2)		(49.8)	(52.3)
Restructuring activities, net					$ (0.1)	$ (6.6)