Property, Plant, and Equipment - Components of property, plant, and equipment (Details) - USD ($) $ in Millions	Sep. 30, 2018		Dec. 31, 2017
Components of property, plant, and equipment
Property, plant and equipment, at cost	$ 8,978.1	[1]	$ 8,385.2
Less accumulated depreciation	(2,440.1)	[1]	(2,250.5)
Property, plant, and equipment, net	6,538.0	[1]	6,134.7
Operating Segments
Components of property, plant, and equipment
Property, plant, and equipment, net	7,369.4		6,944.8
Net deferred profit on railcars sold to the Leasing Group
Components of property, plant, and equipment
Property, plant and equipment, at cost	(1,027.8)		(985.2)
Less accumulated amortization	(196.4)		(175.1)
Property, plant, and equipment, net	(831.4)		(810.1)
Manufacturing/ Corporate
Components of property, plant, and equipment
Property, plant and equipment, at cost	2,081.3		2,046.4
Less accumulated depreciation	(1,136.2)		(1,073.7)
Property, plant, and equipment, net	945.1		972.7
Manufacturing/ Corporate | Land
Components of property, plant, and equipment
Property, plant and equipment, at cost	119.2		122.1
Manufacturing/ Corporate | Buildings and improvements
Components of property, plant, and equipment
Property, plant and equipment, at cost	671.0		668.1
Manufacturing/ Corporate | Machinery and other
Components of property, plant, and equipment
Property, plant and equipment, at cost	1,246.1		1,223.6
Manufacturing/ Corporate | Construction in progress
Components of property, plant, and equipment
Property, plant and equipment, at cost	45.0		32.6
Manufacturing/ Corporate | Operating Segments
Components of property, plant, and equipment
Property, plant, and equipment, net	945.1		972.7
Wholly-owned subsidiaries | Operating Segments | Leasing Group
Components of property, plant, and equipment
Property, plant and equipment, at cost	5,567.9		5,006.4
Less accumulated depreciation	(959.5)		(858.9)
Property, plant, and equipment, net	4,608.4		4,147.5
Wholly-owned subsidiaries | Operating Segments | Machinery and other | Leasing Group
Components of property, plant, and equipment
Property, plant and equipment, at cost	12.8		10.7
Wholly-owned subsidiaries | Operating Segments | Equipment on lease | Leasing Group
Components of property, plant, and equipment
Property, plant and equipment, at cost	5,555.1		4,995.7
Partially-owned subsidiaries
Components of property, plant, and equipment
Property, plant and equipment, at cost	2,019.0	[1]	1,985.9
Less accumulated depreciation	(458.2)	[1]	(418.0)
Partially-owned subsidiaries | Operating Segments | Leasing Group
Components of property, plant, and equipment
Property, plant, and equipment, net	1,815.9		1,824.6
Partially-owned subsidiaries | Operating Segments | Equipment on lease | Leasing Group
Components of property, plant, and equipment
Property, plant and equipment, at cost	2,356.7		2,317.7
Less accumulated depreciation	$ (540.8)		$ (493.1)

[1] (unaudited)