Property, Plant, and Equipment - Components of property, plant, and equipment (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Components of property, plant, and equipment
Property, plant and equipment, at cost	$ 8,882.5	$ 8,253.4
Less accumulated depreciation	(2,012.9)	(1,919.0)
Property, plant, and equipment, net	6,869.6	6,334.4
Operating Segments
Components of property, plant, and equipment
Property, plant, and equipment, net	7,731.5	7,162.1
Net deferred profit on railcars sold to the Leasing Group
Components of property, plant, and equipment
Property, plant and equipment, at cost	(1,078.8)	(1,030.0)
Less accumulated amortization	216.9	202.3
Property, plant, and equipment, net	(861.9)	(827.7)
Manufacturing/ Corporate
Components of property, plant, and equipment
Property, plant and equipment, at cost	988.6	963.2
Less accumulated depreciation	(607.8)	(592.3)
Property, plant, and equipment, net	380.8	370.9
Manufacturing/ Corporate | Land
Components of property, plant, and equipment
Property, plant and equipment, at cost	25.5	24.2
Manufacturing/ Corporate | Buildings and improvements
Components of property, plant, and equipment
Property, plant and equipment, at cost	388.1	385.5
Manufacturing/ Corporate | Machinery and other
Components of property, plant, and equipment
Property, plant and equipment, at cost	529.9	537.2
Manufacturing/ Corporate | Construction in progress
Components of property, plant, and equipment
Property, plant and equipment, at cost	45.1	16.3
Wholly-owned subsidiaries | Railcar Leasing and Management Services Group [Member] | Operating Segments
Components of property, plant, and equipment
Property, plant and equipment, at cost	6,582.0	5,948.3
Less accumulated depreciation	(1,031.9)	(971.8)
Property, plant, and equipment, net	5,550.1	4,976.5
Wholly-owned subsidiaries | Railcar Leasing and Management Services Group [Member] | Machinery and other | Operating Segments
Components of property, plant, and equipment
Property, plant and equipment, at cost	13.8	13.5
Wholly-owned subsidiaries | Railcar Leasing and Management Services Group [Member] | Equipment on lease | Operating Segments
Components of property, plant, and equipment
Property, plant and equipment, at cost	6,568.2	5,934.8
Partially-owned subsidiaries
Components of property, plant, and equipment
Property, plant and equipment, at cost	2,048.3	2,032.0
Less accumulated depreciation	(499.8)	(472.0)
Partially-owned subsidiaries | Railcar Leasing and Management Services Group [Member] | Operating Segments
Components of property, plant, and equipment
Property, plant, and equipment, net	1,800.6	1,814.7
Partially-owned subsidiaries | Railcar Leasing and Management Services Group [Member] | Equipment on lease | Operating Segments
Components of property, plant, and equipment
Property, plant and equipment, at cost	2,390.7	2,371.9
Less accumulated depreciation	$ (590.1)	$ (557.2)