Financial Data of Business Segments (Details) $ in Millions	3 Months Ended
	Mar. 31, 2018 USD ($) Segment	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2015
Segment Reporting Information [Line Items]
Provision for Income Taxes, Equity Method Investment	$ 3.2	$ 3.0
Number of business segments | Segment	4
Profitability
Lease revenue	$ 273.2	272.7
Marine operating revenue	14.2	17.0
Other revenue	17.9	26.4
Total Revenues	305.3	316.1
Maintenance expense	81.2	77.9
Marine operating expense	12.5	12.9
Depreciation	77.4	72.0
Operating lease expense	13.0	15.8
Other operating expense	8.6	9.6
Total Expenses	192.7	188.2
Net gain on asset dispositions	56.1	24.9
Interest expense, net	(39.9)	(39.2)
Other (expense) income	(1.3)	(1.5)
Share of affiliates' earnings (pre-tax)	17.5	11.7
Segment profit (loss)	145.0	123.8
SG&A	44.9	42.7
Income tax benefit	20.6	20.6
Net Income	76.3	57.5
Disposition Gains on Owned Assets	50.0	21.1
Nonoperating Income, Residual Sharing Income	0.4	0.4
Nonremarketing Disposition Gain (Loss)	5.7	3.4
Asset Impairment Charges	0.0	0.0
Selected Balance Sheet Data
Investments in affiliated companies	455.9		$ 441.0
Identifiable assets	7,468.0		7,422.4
Capital Expenditures
Portfolio investments and capital additions	$ (178.4)	(129.0)
Rail North America [Member]
Segment Reporting Information [Line Items]
Leverage level expressed as a ratio of recourse debt to equity	5
Profitability
Lease revenue	$ 219.5	227.2
Marine operating revenue	0.0	0.0
Other revenue	15.8	24.8
Total Revenues	235.3	252.0
Maintenance expense	68.1	67.7
Marine operating expense	0.0	0.0
Depreciation	61.5	59.0
Operating lease expense	13.0	15.0
Other operating expense	6.9	8.1
Total Expenses	149.5	149.8
Net gain on asset dispositions	54.1	23.8
Interest expense, net	(30.2)	(31.1)
Other (expense) income	(0.9)	(2.0)
Share of affiliates' earnings (pre-tax)	0.1	0.1
Segment profit (loss)	108.9	93.0
Disposition Gains on Owned Assets	49.9	21.1
Nonoperating Income, Residual Sharing Income	0.1	0.1
Nonremarketing Disposition Gain (Loss)	4.1	2.6
Asset Impairment Charges	0.0	0.0
Selected Balance Sheet Data
Investments in affiliated companies	6.8		6.8
Identifiable assets	4,965.8		4,915.0
Capital Expenditures
Portfolio investments and capital additions	$ (136.5)	(102.8)
Rail International [Member]
Segment Reporting Information [Line Items]
Leverage level expressed as a ratio of recourse debt to equity	3
Profitability
Lease revenue	$ 52.4	43.3
Marine operating revenue	0.0	0.0
Other revenue	2.0	1.1
Total Revenues	54.4	44.4
Maintenance expense	12.5	10.0
Marine operating expense	0.0	0.0
Depreciation	14.1	11.2
Operating lease expense	0.0	0.0
Other operating expense	1.5	1.2
Total Expenses	28.1	22.4
Net gain on asset dispositions	1.6	0.8
Interest expense, net	(8.7)	(7.9)
Other (expense) income	(0.2)	(1.5)
Share of affiliates' earnings (pre-tax)	0.0	0.0
Segment profit (loss)	19.0	13.4
Disposition Gains on Owned Assets	0.0	0.0
Nonoperating Income, Residual Sharing Income	0.0	0.0
Nonremarketing Disposition Gain (Loss)	1.6	0.8
Asset Impairment Charges	0.0	0.0
Selected Balance Sheet Data
Investments in affiliated companies	0.0		0.0
Identifiable assets	1,382.6		1,332.9
Capital Expenditures
Portfolio investments and capital additions	$ (29.5)	(18.7)
ASC [Member]
Segment Reporting Information [Line Items]
Leverage level expressed as a ratio of recourse debt to equity	1.5
Profitability
Lease revenue	$ 1.0	1.0
Marine operating revenue	9.8	6.4
Other revenue	0.0	0.0
Total Revenues	10.8	7.4
Maintenance expense	0.6	0.2
Marine operating expense	8.2	5.3
Depreciation	0.0	0.1
Operating lease expense	0.0	0.8
Other operating expense	0.0	0.0
Total Expenses	8.8	6.4
Net gain on asset dispositions	0.1	0.0
Interest expense, net	(1.3)	(1.2)
Other (expense) income	0.0	0.0
Share of affiliates' earnings (pre-tax)	0.0	0.0
Segment profit (loss)	0.8	(0.2)
Disposition Gains on Owned Assets	0.1	0.0
Nonoperating Income, Residual Sharing Income	0.0	0.0
Nonremarketing Disposition Gain (Loss)	0.0	0.0
Asset Impairment Charges	0.0	0.0
Selected Balance Sheet Data
Investments in affiliated companies	0.0		0.0
Identifiable assets	298.3		286.7
Capital Expenditures
Portfolio investments and capital additions	$ (11.7)	(7.3)
Portfolio Management [Member]
Segment Reporting Information [Line Items]
Leverage level expressed as a ratio of recourse debt to equity	1
Profitability
Lease revenue	$ 0.3	1.2
Marine operating revenue	4.4	10.6
Other revenue	0.1	0.5
Total Revenues	4.8	12.3
Maintenance expense	0.0	0.0
Marine operating expense	4.3	7.6
Depreciation	1.8	1.7
Operating lease expense	0.0	0.0
Other operating expense	0.2	0.3
Total Expenses	6.3	9.6
Net gain on asset dispositions	0.3	0.3
Interest expense, net	(2.3)	(2.2)
Other (expense) income	0.0	2.3
Share of affiliates' earnings (pre-tax)	17.4	11.6
Segment profit (loss)	13.9	14.7
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
Asset Impairment Charges	0.0	0.0
Selected Balance Sheet Data
Investments in affiliated companies	449.1		434.2
Identifiable assets	597.9		582.8
Capital Expenditures
Portfolio investments and capital additions	0.0	0.0
Other [Member]
Profitability
Lease revenue	0.0	0.0
Marine operating 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	2.6	3.2
Other (expense) income	(0.2)	(0.3)
Share of affiliates' earnings (pre-tax)	0.0	0.0
Segment profit (loss)	2.4	2.9
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
Asset Impairment Charges	0.0	0.0
Selected Balance Sheet Data
Investments in affiliated companies	0.0		0.0
Identifiable assets	223.4		$ 305.0
Capital Expenditures
Portfolio investments and capital additions	(0.7)	(0.2)
Parent [Member]
Profitability
Income tax benefit	$ 23.8	$ 23.6
Cardinal Marine [Domain]
Capital Expenditures
Noncontrolling Interest, Ownership Percentage by Parent				50.00%