Property, Plant, and Equipment - Components of property, plant, and equipment (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Components of property, plant, and equipment
Property, Plant and Equipment, Gross	$ 9,011.8	$ 8,253.4
Less accumulated depreciation	(2,095.1)	(1,919.0)
Property, plant, and equipment, net	6,916.7	6,334.4
Operating Segments
Components of property, plant, and equipment
Property, plant, and equipment, net	7,787.8	7,162.1
Net deferred profit on railcars sold to the Leasing Group
Components of property, plant, and equipment
Property, Plant and Equipment, Gross	(1,094.7)	(1,030.0)
Less accumulated amortization	223.6	202.3
Property, plant, and equipment, net	(871.1)	(827.7)
Manufacturing/ Corporate
Components of property, plant, and equipment
Property, Plant and Equipment, Gross	1,013.8	963.2
Less accumulated depreciation	(617.5)	(592.3)
Property, plant, and equipment, net	396.3	370.9
Manufacturing/ Corporate | Land
Components of property, plant, and equipment
Property, Plant and Equipment, Gross	25.5	24.2
Manufacturing/ Corporate | Buildings and improvements
Components of property, plant, and equipment
Property, Plant and Equipment, Gross	389.0	385.5
Manufacturing/ Corporate | Machinery and other
Components of property, plant, and equipment
Property, Plant and Equipment, Gross	548.9	537.2
Manufacturing/ Corporate | Construction in progress
Components of property, plant, and equipment
Property, Plant and Equipment, Gross	50.4	16.3
Wholly-owned subsidiaries | Railcar Leasing and Management Services Group [Member] | Operating Segments
Components of property, plant, and equipment
Property, Plant and Equipment, Gross	6,691.7	5,948.3
Less accumulated depreciation	(1,094.7)	(971.8)
Property, plant, and equipment, net	5,597.0	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, Gross	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, Gross	6,677.9	5,934.8
Partially-owned subsidiaries
Components of property, plant, and equipment
Property, Plant and Equipment, Gross	2,057.5	2,032.0
Less accumulated depreciation	(513.6)	(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	1,794.5	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, Gross	2,401.0	2,371.9
Less accumulated depreciation	$ (606.5)	$ (557.2)