Segment Information - Financial information for segments (Details) - USD ($) $ in Millions	3 Months Ended						6 Months Ended
	Jun. 30, 2023		Mar. 31, 2023	Jun. 30, 2022		Mar. 31, 2022	Jun. 30, 2023	Jun. 30, 2022
Segment Reporting Information [Line Items]
External Revenue	$ 722.4			$ 416.8			$ 1,364.1	$ 889.5
Revenues, Total	722.4			416.8			1,364.1	889.5
Operating Profit (Loss)	99.1			73.0			168.1	127.8
Restructuring activities, net	1.8			(1.0)			2.2	(1.0)
Other (income) expense	68.2			50.7			131.9	92.6
Provision (benefit) for income taxes	7.4			5.8			(4.1)	8.8
Loss from discontinued operations, net of benefit for income taxes of $0.7, $0.5, $1.5 and $2.5	(2.3)			(3.4)			(5.4)	(10.3)
Loss on sale of discontinued operations, net of benefit for income taxes of $—, $1.0, $— and $1.4	0.0			(4.6)			0.0	(5.7)
Net income	21.2		$ 13.7	8.5		$ 1.9	34.9	10.4
Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues, Total	722.4			416.8			1,364.1	889.5
Operating Profit (Loss)	142.2			119.2			253.0	199.8
Intersegment Eliminations [Member] | Consolidated Subsidiaries, Leasing [Member]
Segment Reporting Information [Line Items]
Intersegment Revenues	(209.6)			(208.9)			(409.0)	(310.2)
Revenues, Total	(209.6)			(208.9)			(409.0)	(310.2)
Operating Profit (Loss)	(13.1)			(20.3)			(29.9)	(29.1)
Intersegment Eliminations [Member] | Consolidated Subsidiaries, Excluding Leasing [Member]
Segment Reporting Information [Line Items]
Intersegment Revenues	(0.2)			(0.2)			(0.4)	(0.4)
Revenues, Total	(0.2)			(0.2)			(0.4)	(0.4)
Operating Profit (Loss)	(0.2)			0.2			0.4	(1.1)
Railcar Leasing and Management Services Group [Member]
Segment Reporting Information [Line Items]
External Revenue	223.0			195.1			426.3	378.0
Railcar Leasing and Management Services Group [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues, Total	223.2			195.3			426.7	378.4
Operating Profit (Loss)	118.5	[1]		105.5	[1]		204.0	185.3
Railcar Leasing and Management Services Group [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment Revenues	0.2			0.2			0.4	0.4
Rail Products Group [Member]
Segment Reporting Information [Line Items]
External Revenue	499.4			221.7			937.8	511.5
Rail Products Group [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues, Total	709.0			430.6			1,346.8	821.7
Operating Profit (Loss)	23.7			13.7			49.0	14.5
Rail Products Group [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment Revenues	209.6			208.9			409.0	310.2
Corporate Segment [Member]
Segment Reporting Information [Line Items]
Operating Profit (Loss)	$ (31.6)			$ (25.1)			$ (57.6)	$ (40.8)

[1] Operating profit includes: depreciation; fleet operating costs, which include maintenance, compliance, freight, and storage; rent and ad valorem taxes; and selling, engineering, and administrative expenses. Amortization of deferred profit on railcars sold from the Rail Products Group to the Leasing Group is included in the operating profit of the Leasing Group, resulting in the recognition of depreciation expense based on our original manufacturing cost of the railcars. Interest expense is not a component of operating profit and includes the effect of hedges.