Property, Plant, and Equipment - Components of property, plant, and equipment (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Components of property, plant, and equipment
Property, plant and equipment, at cost	$ 8,723.2	$ 8,253.4
Less accumulated depreciation	(1,976.4)	(1,919.0)
Property, plant, and equipment, net	6,746.8	6,334.4
Operating Segments
Components of property, plant, and equipment
Property, plant, and equipment, net	7,586.3	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	(1,048.9)	(1,030.0)
Less accumulated amortization	209.4	202.3
Property, plant, and equipment, net	(839.5)	(827.7)
Manufacturing/ Corporate
Components of property, plant, and equipment
Property, plant and equipment, at cost	972.7	963.2
Less accumulated depreciation	(602.9)	(592.3)
Property, plant, and equipment, net	369.8	370.9
Manufacturing/ Corporate | Land
Components of property, plant, and equipment
Property, plant and equipment, at cost	24.2	24.2
Manufacturing/ Corporate | Buildings and improvements
Components of property, plant, and equipment
Property, plant and equipment, at cost	388.4	385.5
Manufacturing/ Corporate | Machinery and other
Components of property, plant, and equipment
Property, plant and equipment, at cost	538.2	537.2
Manufacturing/ Corporate | Construction in progress
Components of property, plant, and equipment
Property, plant and equipment, at cost	21.9	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	6,415.4	5,948.3
Less accumulated depreciation	(1,009.2)	(971.8)
Property, plant, and equipment, net	5,406.2	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	6,401.6	5,934.8
Partially-owned subsidiaries
Components of property, plant, and equipment
Property, plant and equipment, at cost	2,042.3	2,032.0
Less accumulated depreciation	(485.9)	(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	1,810.3	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	2,384.0	2,371.9
Less accumulated depreciation	$ (573.7)	$ (557.2)