Financial Data of Business Segments (Details) $ in Millions	3 Months Ended
	Mar. 31, 2017 USD ($) Segment	Mar. 31, 2016 USD ($)	Dec. 31, 2016 USD ($)
Segment Reporting Information [Line Items]
Provision for Income Taxes, Equity Method Investment	$ 3.0	$ 2.7
Number of business segments | Segment	4
Profitability
Lease revenue	$ 272.7	284.5
Marine operating revenue	17.0	20.3
Other revenue	26.4	29.6
Total Revenues	316.1	334.4
Maintenance expense	77.9	78.5
Marine operating expense	12.9	12.3
Depreciation	72.0	69.3
Operating lease expense	15.8	16.8
Other operating expense	9.6	8.8
Total Expenses	188.2	185.7
Net gain on asset dispositions	24.9	23.2
Interest expense, net	(39.2)	(37.2)
Other (expense) income	(1.3)	(3.3)
Share of affiliates' earnings (pre-tax)	11.7	10.2
Segment profit (loss)	124.0	141.6
SG&A	42.9	38.8
Income tax benefit	20.6	30.8
Net Income	57.5	69.3
Gain (Loss) on Sale of Assets and Asset Impairment Charges	(24.9)	23.2
Disposition Gains on Owned Assets	21.1	20.0
Nonoperating Income, Residual Sharing Income	0.4	1.8
Nonremarketing Disposition Gain (Loss)	3.4	1.4
Asset Impairment Charges	0.0	0.0
Selected Balance Sheet Data
Investments in affiliated companies	396.9		$ 387.0
Identifiable assets	7,096.9		7,105.4
Capital Expenditures
Portfolio investments and capital additions	$ (129.0)	(140.2)
Rail North America [Member]
Segment Reporting Information [Line Items]
Leverage level expressed as a ratio of recourse debt to equity	5
Profitability
Lease revenue	$ 227.2	236.6
Marine operating revenue	0.0	0.0
Other revenue	24.8	27.8
Total Revenues	252.0	264.4
Maintenance expense	67.7	65.8
Marine operating expense	0.0	0.0
Depreciation	59.0	56.5
Operating lease expense	15.0	16.8
Other operating expense	8.1	6.9
Total Expenses	149.8	146.0
Net gain on asset dispositions	23.8	18.6
Interest expense, net	(31.1)	(27.2)
Other (expense) income	(2.0)	(1.3)
Share of affiliates' earnings (pre-tax)	0.1	0.2
Segment profit (loss)	93.0	108.7
Disposition Gains on Owned Assets	21.1	17.6
Nonoperating Income, Residual Sharing Income	0.1	0.3
Nonremarketing Disposition Gain (Loss)	2.6	0.7
Asset Impairment Charges	0.0	0.0
Selected Balance Sheet Data
Investments in affiliated companies	10.5		10.5
Identifiable assets	4,862.5		4,775.6
Capital Expenditures
Portfolio investments and capital additions	$ (102.8)	(112.9)
Rail International [Member]
Segment Reporting Information [Line Items]
Leverage level expressed as a ratio of recourse debt to equity	3
Profitability
Lease revenue	$ 43.3	44.9
Marine operating revenue	0.0	0.0
Other revenue	1.1	1.6
Total Revenues	44.4	46.5
Maintenance expense	10.0	12.5
Marine operating expense	0.0	0.0
Depreciation	11.2	11.1
Operating lease expense	0.0	0.0
Other operating expense	1.2	1.4
Total Expenses	22.4	25.0
Net gain on asset dispositions	0.8	0.7
Interest expense, net	(7.9)	(7.3)
Other (expense) income	(1.5)	(2.2)
Share of affiliates' earnings (pre-tax)	0.0	(0.1)
Segment profit (loss)	13.4	12.6
Disposition Gains on Owned Assets	0.0	0.0
Nonoperating Income, Residual Sharing Income	0.0	0.0
Nonremarketing Disposition Gain (Loss)	0.8	0.7
Asset Impairment Charges	0.0	0.0
Selected Balance Sheet Data
Investments in affiliated companies	1.2		1.2
Identifiable assets	1,169.7		1,128.7
Capital Expenditures
Portfolio investments and capital additions	$ (18.7)	(22.0)
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	6.4	4.1
Other revenue	0.0	0.0
Total Revenues	7.4	5.1
Maintenance expense	0.2	0.2
Marine operating expense	5.3	2.9
Depreciation	0.1	0.0
Operating lease expense	0.8	0.0
Other operating expense	0.0	0.0
Total Expenses	6.4	3.1
Net gain on asset dispositions	0.0	0.0
Interest expense, net	(1.2)	(1.1)
Other (expense) income	0.0	0.0
Share of affiliates' earnings (pre-tax)	0.0	0.0
Segment profit (loss)	(0.2)	0.9
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	306.9		278.8
Capital Expenditures
Portfolio investments and capital additions	$ (7.3)	(4.7)
Portfolio Management [Member]
Segment Reporting Information [Line Items]
Leverage level expressed as a ratio of recourse debt to equity	1
Profitability
Lease revenue	$ 1.2	2.0
Marine operating revenue	10.6	16.2
Other revenue	0.5	0.2
Total Revenues	12.3	18.4
Maintenance expense	0.0	0.0
Marine operating expense	7.6	9.4
Depreciation	1.7	1.7
Operating lease expense	0.0	0.0
Other operating expense	0.3	0.5
Total Expenses	9.6	11.6
Net gain on asset dispositions	0.3	3.9
Interest expense, net	(2.2)	(2.2)
Other (expense) income	2.3	0.0
Share of affiliates' earnings (pre-tax)	11.6	10.1
Segment profit (loss)	14.7	18.6
Disposition Gains on Owned Assets	0.0	2.4
Nonoperating Income, Residual Sharing Income	0.3	1.5
Nonremarketing Disposition Gain (Loss)	0.0	0.0
Asset Impairment Charges	0.0	0.0
Selected Balance Sheet Data
Investments in affiliated companies	385.2		375.3
Identifiable assets	600.0		593.5
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	3.2	0.6
Other (expense) income	(0.1)	0.2
Share of affiliates' earnings (pre-tax)	0.0	0.0
Segment profit (loss)	3.1	0.8
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	157.8		$ 328.8
Capital Expenditures
Portfolio investments and capital additions	(0.2)	(0.6)
Parent [Member]
Profitability
Income tax benefit	$ 23.6	$ 33.5