Property, Plant, and Equipment - Components of property, plant, and equipment (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Property, Plant and Equipment, Net [Abstract]
Property, plant, and equipment, at cost, including partially-owned subsidiaries of $1,938.5 and $1,931.6	$ 9,337.1	$ 9,193.0
Less: accumulated depreciation	(2,288.4)	(2,189.6)
Property, Plant and Equipment, Net	7,048.7	7,003.4
Intersegment Eliminations [Member]
Property, Plant and Equipment, Net [Abstract]
Property, plant, and equipment, at cost, including partially-owned subsidiaries of $1,938.5 and $1,931.6	(1,062.9)	(1,064.7)
NegativeAccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment	258.6	244.4
Property, Plant and Equipment, Net	(804.3)	(820.3)
Railcar Leasing and Management Services Group [Member] | Operating Segments [Member]
Property, Plant and Equipment, Net [Abstract]
Property, Plant and Equipment, Net	7,459.3	7,422.2
Manufacturing and Corporate [Member]
Property, Plant and Equipment, Net [Abstract]
Property, plant, and equipment, at cost, including partially-owned subsidiaries of $1,938.5 and $1,931.6	970.2	979.4
Less: accumulated depreciation	(576.5)	(577.9)
Property, Plant and Equipment, Net	393.7	401.5
Manufacturing and Corporate [Member] | Land
Property, Plant and Equipment, Net [Abstract]
Property, plant, and equipment, at cost, including partially-owned subsidiaries of $1,938.5 and $1,931.6	22.7	23.2
Manufacturing and Corporate [Member] | Buildings and improvements
Property, Plant and Equipment, Net [Abstract]
Property, plant, and equipment, at cost, including partially-owned subsidiaries of $1,938.5 and $1,931.6	437.5	428.6
Manufacturing and Corporate [Member] | Machinery and other
Property, Plant and Equipment, Net [Abstract]
Property, plant, and equipment, at cost, including partially-owned subsidiaries of $1,938.5 and $1,931.6	485.5	485.1
Manufacturing and Corporate [Member] | Construction in progress
Property, Plant and Equipment, Net [Abstract]
Property, plant, and equipment, at cost, including partially-owned subsidiaries of $1,938.5 and $1,931.6	24.5	42.5
Wholly-owned subsidiaries | Railcar Leasing and Management Services Group [Member] | Operating Segments [Member]
Property, Plant and Equipment, Net [Abstract]
Property, plant, and equipment, at cost, including partially-owned subsidiaries of $1,938.5 and $1,931.6	7,174.2	7,030.1
Less: accumulated depreciation	(1,320.5)	(1,234.2)
Property, Plant and Equipment, Net	5,853.7	5,795.9
Wholly-owned subsidiaries | Railcar Leasing and Management Services Group [Member] | Machinery and other | Operating Segments [Member]
Property, Plant and Equipment, Net [Abstract]
Property, plant, and equipment, at cost, including partially-owned subsidiaries of $1,938.5 and $1,931.6	19.4	19.5
Wholly-owned subsidiaries | Railcar Leasing and Management Services Group [Member] | Equipment on lease | Operating Segments [Member]
Property, Plant and Equipment, Net [Abstract]
Property, plant, and equipment, at cost, including partially-owned subsidiaries of $1,938.5 and $1,931.6	7,154.8	7,010.6
Partially-owned subsidiaries
Property, Plant and Equipment, Net [Abstract]
Property, plant, and equipment, at cost, including partially-owned subsidiaries of $1,938.5 and $1,931.6	1,938.5	1,931.6
Less: accumulated depreciation	(549.5)	(525.7)
Partially-owned subsidiaries | Railcar Leasing and Management Services Group [Member] | Operating Segments [Member]
Property, Plant and Equipment, Net [Abstract]
Property, plant, and equipment, at cost, including partially-owned subsidiaries of $1,938.5 and $1,931.6	2,255.6	2,248.2
Less: accumulated depreciation	(650.0)	(621.9)
Property, Plant and Equipment, Net	$ 1,605.6	$ 1,626.3