Segment Information - Financial information for segments (Details) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2018 USD ($) segment	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Segment Reporting Information [Line Items]
Number of Reportable Segments | segment									3
Revenues	$ 735.0	$ 606.9	$ 634.0	$ 533.2	$ 615.4	$ 655.7	$ 595.7	$ 530.6	$ 2,509.1	$ 2,397.4	$ 3,089.8
Operating Profit (Loss)	89.8	$ 75.2	$ 88.0	$ 62.1	115.5	$ 105.1	$ 83.1	$ 64.6	315.1	368.3	478.9
Assets	7,989.2				9,543.2				7,989.2	9,543.2
Disposal Group, Including Discontinued Operation, Assets	0.0				1,654.2				0.0	1,654.2
Depreciation & Amortization									251.9	229.7	217.3
Capital Expenditures									985.6	630.3	848.6
Intersegment
Segment Reporting Information [Line Items]
Revenues									1,041.7	822.9	1,121.7
Total
Segment Reporting Information [Line Items]
Revenues									3,550.8	3,220.3	4,211.5
Operating Profit (Loss)									558.9	642.2	811.0
Assets	8,373.6				7,394.2				8,373.6	7,394.2
Depreciation & Amortization									242.0	220.2	208.7
Capital Expenditures									981.6	622.7	830.6
Corporate
Segment Reporting Information [Line Items]
Operating Profit (Loss)									(149.0)	(175.1)	(153.0)
Assets	443.4				1,305.8				443.4	1,305.8
Depreciation & Amortization									9.9	9.6	8.7
Capital Expenditures									4.0	7.6	18.0
Rail Products Group
Segment Reporting Information [Line Items]
Revenues									1,356.4	1,254.5	1,954.5
Assets	1,039.1				901.9				1,039.1	901.9
Depreciation & Amortization									30.3	35.1	38.3
Capital Expenditures									16.0	4.9	18.5
Rail Products Group | Intersegment
Segment Reporting Information [Line Items]
Revenues									990.3	789.5	1,073.3
Rail Products Group | Total
Segment Reporting Information [Line Items]
Revenues									2,346.7	2,044.0	3,027.8
Operating Profit (Loss)									172.1	196.3	449.4
Railcar Leasing and Management Services Group
Segment Reporting Information [Line Items]
Revenues									842.0	842.2	824.9
Assets	7,096.0				6,267.9				7,096.0	6,267.9
Depreciation & Amortization									196.6	172.3	156.2
Capital Expenditures									948.3	608.3	799.1
Railcar Leasing and Management Services Group | Intersegment
Segment Reporting Information [Line Items]
Revenues									0.8	1.0	2.1
Railcar Leasing and Management Services Group | Total
Segment Reporting Information [Line Items]
Revenues									842.8	843.2	827.0
Operating Profit (Loss)									351.1	444.5	360.1
Depreciation & Amortization									196.6	172.3	156.2
All Other
Segment Reporting Information [Line Items]
Revenues									310.7	300.7	310.4
Assets	238.5				224.4				238.5	224.4
Depreciation & Amortization									15.1	12.8	14.2
Capital Expenditures									17.3	9.5	13.0
All Other | Intersegment
Segment Reporting Information [Line Items]
Revenues									50.6	32.4	46.3
All Other | Total
Segment Reporting Information [Line Items]
Revenues									361.3	333.1	356.7
Operating Profit (Loss)									35.7	1.4	1.5
Eliminations - Lease subsidiary
Segment Reporting Information [Line Items]
Assets	(827.7)				(800.7)				(827.7)	(800.7)
Depreciation & Amortization									0.0	0.0	0.0
Capital Expenditures									0.0	0.0	0.0
Eliminations - Lease subsidiary | Intersegment
Segment Reporting Information [Line Items]
Revenues									(990.0)	(788.6)	(1,070.4)
Operating Profit (Loss)									(95.1)	(96.5)	(180.7)
Eliminations - Other
Segment Reporting Information [Line Items]
Assets	$ (0.1)				$ (10.3)				(0.1)	(10.3)
Depreciation & Amortization									0.0	(0.1)	(0.1)
Capital Expenditures									0.0	0.0	0.0
Eliminations - Other | Intersegment
Segment Reporting Information [Line Items]
Revenues									(51.7)	(34.3)	(51.3)
Operating Profit (Loss)									$ 0.3	$ (2.3)	$ 1.6