Segment Information - Financial information for segments (Details) - USD ($) $ in Millions		3 Months Ended						9 Months Ended
		Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Sep. 30, 2023	Sep. 30, 2022
Segment Reporting Information [Line Items]
External Revenue		$ 821.3			$ 496.6			$ 2,185.4	$ 1,386.1
Revenues, Total		821.3			496.6			2,185.4	1,386.1
Operating Profit (Loss)		100.2			92.7			268.3	220.5
Restructuring activities, net		0.0			0.0			2.2	(1.0)
Other (income) expense		67.9			54.4			199.8	147.0
Provision (benefit) for income taxes		6.0			8.6			1.9	17.4
Loss from discontinued operations, net of benefit for income taxes of $0.7, $1.0, $2.2 and $3.5		(2.7)			(3.4)			(8.1)	(13.7)
Loss on sale of discontinued operations, net of benefit for income taxes of $—, $—, $— and $1.4		0.0			0.0			0.0	(5.7)
Net income		23.6	$ 21.2	$ 13.7	26.3	$ 8.5	$ 1.9	58.5	36.7
Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues, Total		821.3			496.6			2,185.4	1,386.1
Operating Profit (Loss)		127.8			133.9			380.8	333.7
Intersegment Eliminations [Member] | Consolidated Subsidiaries, Leasing [Member]
Segment Reporting Information [Line Items]
Intersegment Revenues		(83.2)			(295.3)			(492.2)	(605.5)
Revenues, Total		(83.2)			(295.3)			(492.2)	(605.5)
Operating Profit (Loss)		(2.4)			(19.6)			(32.3)	(48.7)
Intersegment Eliminations [Member] | Consolidated Subsidiaries, Excluding Leasing [Member]
Segment Reporting Information [Line Items]
Intersegment Revenues		(0.3)			(0.2)			(0.7)	(0.6)
Revenues, Total		(0.3)			(0.2)			(0.7)	(0.6)
Operating Profit (Loss)		0.0			(0.2)			0.4	(1.3)
Railcar Leasing and Management Services Group [Member]
Segment Reporting Information [Line Items]
External Revenue		222.3			194.6			648.6	572.6
Railcar Leasing and Management Services Group [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues, Total		222.6			194.8			649.3	573.2
Operating Profit (Loss)	[1]	88.6			107.9			292.6	293.2
Railcar Leasing and Management Services Group [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment Revenues		0.3			0.2			0.7	0.6
Rail Products Group [Member]
Segment Reporting Information [Line Items]
External Revenue		599.0			302.0			1,536.8	813.5
Rail Products Group [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues, Total		682.2			597.3			2,029.0	1,419.0
Operating Profit (Loss)		39.2			26.0			88.2	40.5
Rail Products Group [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Intersegment Revenues		83.2			295.3			492.2	605.5
Corporate Segment [Member]
Segment Reporting Information [Line Items]
Operating Profit (Loss)		$ (25.2)			$ (21.4)			$ (82.8)	$ (62.2)

[1] Operating profit includes: depreciation and amortization; 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.