Property, Plant, and Equipment - Components of property, plant, and equipment (Details) - USD ($) $ in Millions		Sep. 30, 2024	Dec. 31, 2023
Property, Plant and Equipment, Net [Abstract]
Property, plant, and equipment, at cost, including partially-owned subsidiaries of $1,923.2 and $1,922.5		$ 9,643.0	$ 9,539.6
Less: accumulated depreciation		(2,714.4)	(2,534.8)
Property, Plant and Equipment, Net		6,928.6	7,004.8
Railcars on Lease [Member]
Property, Plant and Equipment, Net [Abstract]
Property, Plant and Equipment, Net		6,582.7	6,654.8
Railcars on Lease [Member] | Intersegment Eliminations [Member]
Property, Plant and Equipment, Net [Abstract]
Property, plant, and equipment, at cost, including partially-owned subsidiaries of $1,923.2 and $1,922.5	[1]	(1,059.0)	(1,061.3)
Property, Plant and Equipment, Net		(727.4)	(750.2)
Negative Accumulated Depreciation PP&E- Deferred Profit		331.6	311.1
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 $1,923.2 and $1,922.5		7,612.6	7,536.7
Less: accumulated depreciation		(1,734.5)	(1,604.9)
Property, Plant and Equipment, Net		5,878.1	5,931.8
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 $1,923.2 and $1,922.5		2,236.8	2,236.6
Less: accumulated depreciation		(804.8)	(763.4)
Property, Plant and Equipment, Net		1,432.0	1,473.2
Operating & Administrative Assets [Member]
Property, Plant and Equipment, Net [Abstract]
Property, plant, and equipment, at cost, including partially-owned subsidiaries of $1,923.2 and $1,922.5		852.6	827.6
Less: accumulated depreciation		(506.7)	(477.6)
Property, Plant and Equipment, Net		345.9	350.0
Operating & Administrative Assets [Member] | Land
Property, Plant and Equipment, Net [Abstract]
Property, plant, and equipment, at cost, including partially-owned subsidiaries of $1,923.2 and $1,922.5		16.3	16.1
Operating & Administrative Assets [Member] | Buildings and improvements
Property, Plant and Equipment, Net [Abstract]
Property, plant, and equipment, at cost, including partially-owned subsidiaries of $1,923.2 and $1,922.5		392.5	380.4
Operating & Administrative Assets [Member] | Machinery and other
Property, Plant and Equipment, Net [Abstract]
Property, plant, and equipment, at cost, including partially-owned subsidiaries of $1,923.2 and $1,922.5		429.4	419.8
Operating & Administrative Assets [Member] | Construction in progress
Property, Plant and Equipment, Net [Abstract]
Property, plant, and equipment, at cost, including partially-owned subsidiaries of $1,923.2 and $1,922.5		$ 14.4	$ 11.3

[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.