Financial Data of Business Segments (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019 USD ($) Segment	Mar. 31, 2018 USD ($)	Dec. 31, 2018 USD ($)
Segment Reporting Information [Line Items]
Provision for Income Taxes, Equity Method Investment	$ 3.5	$ 3.2
Number of business segments | Segment	4
Profitability
Lease revenue	$ 274.4	273.2
Other revenue	29.5	17.9
Total Revenues	317.0	305.3
Maintenance expense	81.2	81.2
Marine operating expense	12.1	12.5
Depreciation	79.9	77.4
Operating lease expense	13.7	13.0
Other operating expense	8.0	8.6
Total Expenses	194.9	192.7
Net gain on asset dispositions	8.9	56.1
Interest expense, net	(46.5)	(39.9)
Other (expense) income	(3.2)	(1.3)
Share of affiliates' earnings (pre-tax)	18.2	17.5
Segment profit (loss)	99.5	145.0
SG&A	46.1	44.9
Income tax benefit	8.4	20.6
Net Income	41.5	76.3
Disposition Gains on Owned Assets	9.7	50.0
Nonoperating Income, Residual Sharing Income	0.4	0.4
Nonremarketing Disposition Gain (Loss)	(1.2)	5.7
Selected Balance Sheet Data
Investments in affiliated companies	480.0		$ 464.5
Identifiable assets	8,240.2		7,616.7
Capital Expenditures
Portfolio investments and capital additions	(147.3)	(178.4)
Revenue Recognition, Cargo and Freight, Policy [Policy Text Block]	13.1	14.2
Rail North America [Member]
Profitability
Lease revenue	220.9	219.5
Other revenue	27.4	15.8
Total Revenues	248.3	235.3
Maintenance expense	68.8	68.1
Marine operating expense	0.0	0.0
Depreciation	64.3	61.5
Operating lease expense	13.7	13.0
Other operating expense	6.4	6.9
Total Expenses	153.2	149.5
Net gain on asset dispositions	8.2	54.1
Interest expense, net	(34.2)	(30.2)
Other (expense) income	(0.7)	(0.9)
Share of affiliates' earnings (pre-tax)	0.0	0.1
Segment profit (loss)	68.4	108.9
Disposition Gains on Owned Assets	9.7	49.9
Nonoperating Income, Residual Sharing Income	0.1	0.1
Nonremarketing Disposition Gain (Loss)	(1.6)	4.1
Selected Balance Sheet Data
Investments in affiliated companies	0.2		0.2
Identifiable assets	5,656.7		5,236.6
Capital Expenditures
Portfolio investments and capital additions	(99.0)	(136.5)
Revenue Recognition, Cargo and Freight, Policy [Policy Text Block]	0.0	0.0
Rail International [Member]
Profitability
Lease revenue	52.2	52.4
Other revenue	2.0	2.0
Total Revenues	54.2	54.4
Maintenance expense	12.1	12.5
Marine operating expense	0.0	0.0
Depreciation	14.0	14.1
Operating lease expense	0.0	0.0
Other operating expense	1.5	1.5
Total Expenses	27.6	28.1
Net gain on asset dispositions	0.4	1.6
Interest expense, net	(9.9)	(8.7)
Other (expense) income	(2.3)	(0.2)
Share of affiliates' earnings (pre-tax)	0.0	0.0
Segment profit (loss)	14.8	19.0
Disposition Gains on Owned Assets	0.0	0.0
Nonoperating Income, Residual Sharing Income	0.0	0.0
Nonremarketing Disposition Gain (Loss)	0.4	1.6
Selected Balance Sheet Data
Investments in affiliated companies	0.0		0.0
Identifiable assets	1,365.2		1,363.2
Capital Expenditures
Portfolio investments and capital additions	(33.1)	(29.5)
Revenue Recognition, Cargo and Freight, Policy [Policy Text Block]	0.0	0.0
ASC [Member]
Profitability
Lease revenue	1.0	1.0
Other revenue	0.0	0.0
Total Revenues	11.7	10.8
Maintenance expense	0.3	0.6
Marine operating expense	7.5	8.2
Depreciation	0.0	0.0
Operating lease expense	0.0	0.0
Other operating expense	0.0	0.0
Total Expenses	7.8	8.8
Net gain on asset dispositions	0.0	0.1
Interest expense, net	(1.4)	(1.3)
Other (expense) income	0.0	0.0
Share of affiliates' earnings (pre-tax)	0.0	0.0
Segment profit (loss)	2.5	0.8
Disposition Gains on Owned Assets	0.0	0.1
Nonoperating Income, Residual Sharing Income	0.0	0.0
Nonremarketing Disposition Gain (Loss)	0.0	0.0
Selected Balance Sheet Data
Investments in affiliated companies	0.0		0.0
Identifiable assets	311.2		297.8
Capital Expenditures
Portfolio investments and capital additions	(14.5)	(11.7)
Revenue Recognition, Cargo and Freight, Policy [Policy Text Block]	10.7	9.8
Portfolio Management [Member]
Profitability
Lease revenue	0.3	0.3
Other revenue	0.1	0.1
Total Revenues	2.8	4.8
Maintenance expense	0.0	0.0
Marine operating expense	4.6	4.3
Depreciation	1.6	1.8
Operating lease expense	0.0	0.0
Other operating expense	0.1	0.2
Total Expenses	6.3	6.3
Net gain on asset dispositions	0.3	0.3
Interest expense, net	(2.7)	(2.3)
Other (expense) income	0.0	0.0
Share of affiliates' earnings (pre-tax)	18.2	17.4
Segment profit (loss)	12.3	13.9
Disposition Gains on Owned Assets	0.0	0.0
Nonoperating Income, Residual Sharing Income	0.3	0.3
Nonremarketing Disposition Gain (Loss)	0.0	0.0
Selected Balance Sheet Data
Investments in affiliated companies	479.8		464.3
Identifiable assets	618.3		606.8
Capital Expenditures
Portfolio investments and capital additions	0.0	0.0
Revenue Recognition, Cargo and Freight, Policy [Policy Text Block]	2.4	4.4
Other [Member]
Profitability
Lease revenue	0.0	0.0
Other revenue	0.0	0.0
Total Revenues	0.0	0.0
Maintenance expense	0.0	0.0
Marine operating expense	0.0	0.0
Depreciation	0.0	0.0
Operating lease expense	0.0	0.0
Other operating expense	0.0	0.0
Total Expenses	0.0	0.0
Net gain on asset dispositions	0.0	0.0
Interest expense, net	1.7	2.6
Other (expense) income	(0.2)	(0.2)
Share of affiliates' earnings (pre-tax)	0.0	0.0
Segment profit (loss)	1.5	2.4
Disposition Gains on Owned Assets	0.0	0.0
Nonoperating Income, Residual Sharing Income	0.0	0.0
Nonremarketing Disposition Gain (Loss)	0.0	0.0
Selected Balance Sheet Data
Investments in affiliated companies	0.0		0.0
Identifiable assets	288.8		$ 112.3
Capital Expenditures
Portfolio investments and capital additions	(0.7)	(0.7)
Revenue Recognition, Cargo and Freight, Policy [Policy Text Block]	0.0	0.0
Parent [Member]
Profitability
Income tax benefit	$ 11.9	$ 23.8