Property, Plant, and Equipment - Components of property, plant, and equipment (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Property, plant and equipment, at cost	$ 8,253.4	$ 7,330.5
Less: accumulated depreciation	(1,919.0)	(1,772.7)
Property, plant, and equipment, net	6,334.4	5,557.8
Operating Segments
Property, Plant and Equipment [Line Items]
Property, plant, and equipment, net	7,162.1	6,358.5
Net deferred profit on railcars sold to Leasing Group
Property, Plant and Equipment [Line Items]
Property, plant and equipment, at cost	(1,030.0)	(974.9)
NegativeAccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment	(202.3)	(174.2)
Property, plant, and equipment, net	(827.7)	(800.7)
Partially-owned subsidiaries
Property, Plant and Equipment [Line Items]
Property, plant and equipment, at cost	2,032.0	1,985.9
Less: accumulated depreciation	(472.0)	(418.0)
Partially-owned subsidiaries | Operating Segments | Leasing Group
Property, Plant and Equipment [Line Items]
Property, plant, and equipment, net	1,814.7	1,822.7
Partially-owned subsidiaries | Operating Segments | Equipment on lease | Leasing Group
Property, Plant and Equipment [Line Items]
Property, plant and equipment, at cost	2,371.9	2,315.5
Less: accumulated depreciation	(557.2)	(492.8)
Wholly-owned subsidiaries | Operating Segments | Leasing Group
Property, Plant and Equipment [Line Items]
Property, plant and equipment, at cost	5,948.3	4,998.3
Less: accumulated depreciation	(971.8)	(858.3)
Property, plant, and equipment, net	4,976.5	4,140.0
Wholly-owned subsidiaries | Operating Segments | Machinery and other | Leasing Group
Property, Plant and Equipment [Line Items]
Property, plant and equipment, at cost	13.5	10.7
Wholly-owned subsidiaries | Operating Segments | Equipment on lease | Leasing Group
Property, Plant and Equipment [Line Items]
Property, plant and equipment, at cost	5,934.8	4,987.6
Manufacturing/Corporate
Property, Plant and Equipment [Line Items]
Property, plant and equipment, at cost	963.2	991.6
Less: accumulated depreciation	(592.3)	(595.8)
Property, plant, and equipment, net	370.9	395.8
Manufacturing/Corporate | Land
Property, Plant and Equipment [Line Items]
Property, plant and equipment, at cost	24.2	25.4
Manufacturing/Corporate | Buildings and improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment, at cost	385.5	407.7
Manufacturing/Corporate | Machinery and other
Property, Plant and Equipment [Line Items]
Property, plant and equipment, at cost	537.2	550.2
Manufacturing/Corporate | Construction in progress
Property, Plant and Equipment [Line Items]
Property, plant and equipment, at cost	16.3	8.3
Manufacturing/Corporate | Operating Segments
Property, Plant and Equipment [Line Items]
Property, plant, and equipment, net	$ 370.9	$ 395.8