Property, Plant, and Equipment - Components of property, plant, and equipment (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Components of property, plant, and equipment
Property, Plant and Equipment, Gross	$ 9,335.7	$ 9,272.5
Less accumulated depreciation	(2,217.0)	(2,161.9)
Property, plant, and equipment, net	7,118.7	7,110.6
Intersegment Eliminations [Member]
Components of property, plant, and equipment
Property, Plant and Equipment, Gross	(1,138.5)	(1,135.8)
Less accumulated amortization	238.8	232.0
Property, plant, and equipment, net	(899.7)	(903.8)
Railcar Leasing and Management Services Group [Member] | Operating Segments
Components of property, plant, and equipment
Property, plant, and equipment, net	7,614.1	7,605.6
Manufacturing/ Corporate
Components of property, plant, and equipment
Property, Plant and Equipment, Gross	1,045.5	1,040.4
Less accumulated depreciation	(641.2)	(631.6)
Property, plant, and equipment, net	404.3	408.8
Manufacturing/ Corporate | Land
Components of property, plant, and equipment
Property, Plant and Equipment, Gross	28.6	28.4
Manufacturing/ Corporate | Buildings and improvements
Components of property, plant, and equipment
Property, Plant and Equipment, Gross	400.9	402.2
Manufacturing/ Corporate | Machinery and other
Components of property, plant, and equipment
Property, Plant and Equipment, Gross	544.7	546.7
Manufacturing/ Corporate | Construction in progress
Components of property, plant, and equipment
Property, Plant and Equipment, Gross	71.3	63.1
Wholly-owned subsidiaries | Railcar Leasing and Management Services Group [Member] | Operating Segments
Components of property, plant, and equipment
Property, Plant and Equipment, Gross	7,013.7	6,957.9
Less accumulated depreciation	(1,176.2)	(1,139.0)
Property, plant, and equipment, net	5,837.5	5,818.9
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	13.7	13.7
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	7,000.0	6,944.2
Partially-owned subsidiaries
Components of property, plant, and equipment
Property, Plant and Equipment, Gross	2,069.6	2,065.3
Less accumulated depreciation	(540.5)	(527.7)
Partially-owned subsidiaries | Railcar Leasing and Management Services Group [Member] | Operating Segments
Components of property, plant, and equipment
Property, plant, and equipment, net	1,776.6	1,786.7
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	2,415.0	2,410.0
Less accumulated depreciation	$ (638.4)	$ (623.3)