Property, Plant, and Equipment - Components of property, plant, and equipment (Details) - USD ($) $ in Millions		Sep. 30, 2025	Dec. 31, 2024
Property, Plant and Equipment, Net [Abstract]
Property, plant, and equipment, at cost, including partially-owned subsidiaries of $1,928.5 and $1,920.5		$ 10,124.4	$ 9,751.1
Less: accumulated depreciation		(2,934.9)	(2,763.0)
Property, Plant and Equipment, Net		7,189.5	6,988.1
Railcars on Lease [Member]
Property, Plant and Equipment, Net [Abstract]
Property, Plant and Equipment, Net		6,832.4	6,631.6
Railcars on Lease [Member] | Intersegment Eliminations [Member]
Property, Plant and Equipment, Net [Abstract]
Property, plant, and equipment, at cost, including partially-owned subsidiaries of $1,928.5 and $1,920.5	[1]	(1,084.8)	(1,069.8)
Property, Plant and Equipment, Net		(724.7)	(732.5)
Negative Accumulated Depreciation PP&E- Deferred Profit		360.1	337.3
Wholly-owned subsidiaries | Railcars on Lease [Member] | Operating Segments [Member]
Property, Plant and Equipment, Net [Abstract]
Property, plant, and equipment, at cost, including partially-owned subsidiaries of $1,928.5 and $1,920.5		8,082.3	7,715.0
Less: accumulated depreciation		(1,905.3)	(1,766.9)
Property, Plant and Equipment, Net		6,177.0	5,948.1
Partially-owned subsidiaries | Railcars on Lease [Member] | Operating Segments [Member]
Property, Plant and Equipment, Net [Abstract]
Property, plant, and equipment, at cost, including partially-owned subsidiaries of $1,928.5 and $1,920.5		2,240.8	2,233.1
Less: accumulated depreciation		(860.7)	(817.1)
Property, Plant and Equipment, Net		1,380.1	1,416.0
Operating & Administrative Assets [Member]
Property, Plant and Equipment, Net [Abstract]
Property, plant, and equipment, at cost, including partially-owned subsidiaries of $1,928.5 and $1,920.5		886.1	872.8
Less: accumulated depreciation		(529.0)	(516.3)
Property, Plant and Equipment, Net		357.1	356.5
Operating & Administrative Assets [Member] | Land
Property, Plant and Equipment, Net [Abstract]
Property, plant, and equipment, at cost, including partially-owned subsidiaries of $1,928.5 and $1,920.5		16.1	16.3
Operating & Administrative Assets [Member] | Buildings and improvements
Property, Plant and Equipment, Net [Abstract]
Property, plant, and equipment, at cost, including partially-owned subsidiaries of $1,928.5 and $1,920.5		406.3	403.2
Operating & Administrative Assets [Member] | Machinery and other
Property, Plant and Equipment, Net [Abstract]
Property, plant, and equipment, at cost, including partially-owned subsidiaries of $1,928.5 and $1,920.5		435.8	441.8
Operating & Administrative Assets [Member] | Construction in progress
Property, Plant and Equipment, Net [Abstract]
Property, plant, and equipment, at cost, including partially-owned subsidiaries of $1,928.5 and $1,920.5		$ 27.9	$ 11.5

[1] Includes deferred profit related to new railcar additions, sustainable railcar conversions, railcar modifications, and other betterments. The deferred profit is subsequently eliminated in consolidation.