Property, Plant, and Equipment - Components of property, plant, and equipment (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Property, Plant and Equipment, Net [Abstract]
Property, Plant and Equipment, Gross	$ 8,939.5	$ 9,272.5
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	(2,155.1)	(2,161.9)
Property, Plant and Equipment, Net	6,784.4	7,110.6
Intersegment Eliminations [Member]
Property, Plant and Equipment, Net [Abstract]
Property, Plant and Equipment, Gross	(1,062.4)	(1,135.8)
NegativeAccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment	229.8	232.0
Property, Plant and Equipment, Net	(832.6)	(903.8)
Railcar Leasing and Management Services Group [Member] | Operating Segments [Member]
Property, Plant and Equipment, Net [Abstract]
Property, Plant and Equipment, Net	7,205.3	7,605.6
Manufacturing and Corporate [Member]
Property, Plant and Equipment, Net [Abstract]
Property, Plant and Equipment, Gross	1,056.1	1,040.4
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	(644.4)	(631.6)
Property, Plant and Equipment, Net	411.7	408.8
Manufacturing and Corporate [Member] | Land
Property, Plant and Equipment, Net [Abstract]
Property, Plant and Equipment, Gross	28.6	28.4
Manufacturing and Corporate [Member] | Buildings and improvements
Property, Plant and Equipment, Net [Abstract]
Property, Plant and Equipment, Gross	407.1	402.2
Manufacturing and Corporate [Member] | Machinery and other
Property, Plant and Equipment, Net [Abstract]
Property, Plant and Equipment, Gross	544.0	546.7
Manufacturing and Corporate [Member] | Construction in progress
Property, Plant and Equipment, Net [Abstract]
Property, Plant and Equipment, Gross	76.4	63.1
Wholly-owned subsidiaries | Railcar Leasing and Management Services Group [Member] | Operating Segments [Member]
Property, Plant and Equipment, Net [Abstract]
Property, Plant and Equipment, Gross	6,706.1	6,957.9
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	(1,149.0)	(1,139.0)
Property, Plant and Equipment, Net	5,557.1	5,818.9
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, Gross	13.9	13.7
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, Gross	6,692.2	6,944.2
Partially-owned subsidiaries
Property, Plant and Equipment, Net [Abstract]
Property, Plant and Equipment, Gross	1,923.8	2,065.3
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	(499.7)	(527.7)
Partially-owned subsidiaries | Railcar Leasing and Management Services Group [Member] | Operating Segments [Member]
Property, Plant and Equipment, Net [Abstract]
Property, Plant and Equipment, Net	1,648.2	1,786.7
Partially-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, Gross	2,239.7	2,410.0
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	$ (591.5)	$ (623.3)