Financial Data of Business Segments (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) Segment	Sep. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)
Segment Reporting Information [Line Items]
Provision for Income Taxes, Equity Method Investment	$ 2.7	$ (0.1)	$ 5.7	$ 4.0
Number of business segments | Segment			4
Profitability
Lease revenue	276.6	281.8	$ 823.4	847.5
Marine operating revenue	62.9	62.1	135.0	139.7
Other revenue	20.1	19.0	65.7	69.0
Total Revenues	359.6	362.9	1,024.1	1,056.2
Maintenance expense	84.9	79.6	247.7	244.6
Marine operating expense	38.9	39.2	89.8	88.9
Depreciation	78.6	75.9	227.9	221.0
Operating lease expense	15.8	19.2	46.8	54.5
Other operating expense	8.5	10.1	25.9	33.7
Total Expenses	226.7	224.0	638.1	642.7
Net gain on asset dispositions	9.4	62.7	56.3	122.8
Interest expense, net	(40.2)	(36.2)	(119.4)	(109.9)
Other (expense) income	(2.1)	4.3	(4.5)	(2.9)
Share of affiliates' earnings (pre-tax)	16.1	15.1	40.2	33.1
Segment profit (loss)	116.1	184.8	358.6	456.6
SG&A	42.8	48.1	128.8	127.8
Income tax benefit	20.4	41.1	60.3	98.6
Net Income	49.0	95.7	159.9	226.2
Gain (Loss) on Sale of Assets and Asset Impairment Charges	9.4	62.7	56.3	122.8
Disposition Gains on Owned Assets	7.6	11.6	41.4	36.7
Nonoperating Income, Residual Sharing Income	0.5	49.7	9.8	83.2
Nonremarketing Disposition Gain (Loss)	1.3	1.4	7.0	4.7
Asset Impairment Charges			(1.9)	(1.8)
Selected Balance Sheet Data
Investments in affiliated companies	449.3		449.3		$ 387.0
Identifiable assets	7,261.9		7,261.9		7,105.4
Capital Expenditures
Portfolio investments and capital additions	(163.7)	(120.4)	$ (459.0)	(442.6)
Rail North America [Member]
Segment Reporting Information [Line Items]
Leverage level expressed as a ratio of recourse debt to equity			5
Profitability
Lease revenue	224.5	233.0	$ 677.4	703.0
Marine operating revenue	0.0	0.0	0.0	0.0
Other revenue	17.9	17.3	60.0	63.5
Total Revenues	242.4	250.3	737.4	766.5
Maintenance expense	66.1	62.8	202.3	196.2
Marine operating expense	0.0	0.0	0.0	0.0
Depreciation	60.1	58.4	178.8	173.0
Operating lease expense	15.5	17.2	45.3	50.6
Other operating expense	7.3	8.6	21.7	25.0
Total Expenses	149.0	147.0	448.1	444.8
Net gain on asset dispositions	8.1	13.1	42.6	36.4
Interest expense, net	(30.5)	27.1	(90.1)	81.2
Other (expense) income	(0.9)	(1.4)	(4.1)	(3.8)
Share of affiliates' earnings (pre-tax)	0.1	0.0	0.4	0.3
Segment profit (loss)	70.2	87.9	238.1	273.4
Disposition Gains on Owned Assets	7.5	11.9	39.5	32.5
Nonoperating Income, Residual Sharing Income	0.2	0.3	0.5	0.7
Nonremarketing Disposition Gain (Loss)	0.4	0.9	4.5	3.2
Asset Impairment Charges			(1.9)	0.0
Selected Balance Sheet Data
Investments in affiliated companies	9.8		9.8		10.5
Identifiable assets	4,841.2		4,841.2		4,775.6
Capital Expenditures
Portfolio investments and capital additions	(103.3)	(108.4)	$ (333.7)	(366.7)
Rail International [Member]
Segment Reporting Information [Line Items]
Leverage level expressed as a ratio of recourse debt to equity			3
Profitability
Lease revenue	50.3	46.6	$ 139.8	136.8
Marine operating revenue	0.0	0.0	0.0	0.0
Other revenue	2.0	1.6	4.7	4.8
Total Revenues	52.3	48.2	144.5	141.6
Maintenance expense	11.1	10.7	30.8	36.1
Marine operating expense	0.0	0.0	0.0	0.0
Depreciation	12.8	11.6	35.8	34.2
Operating lease expense	0.0	0.0	0.0	0.0
Other operating expense	1.1	1.2	3.5	3.8
Total Expenses	25.0	23.5	70.1	74.1
Net gain on asset dispositions	1.0	0.5	2.6	1.5
Interest expense, net	(8.5)	7.3	(24.5)	21.9
Other (expense) income	0.3	5.5	(2.3)	2.0
Share of affiliates' earnings (pre-tax)	0.0	(0.1)	(0.1)	(0.2)
Segment profit (loss)	20.1	23.3	50.1	48.9
Disposition Gains on Owned Assets	0.1	0.0	0.1	0.0
Nonoperating Income, Residual Sharing Income	0.0	0.0	0.0	0.0
Nonremarketing Disposition Gain (Loss)	0.9	0.5	2.5	1.5
Asset Impairment Charges			0.0	0.0
Selected Balance Sheet Data
Investments in affiliated companies	0.0		0.0		1.2
Identifiable assets	1,290.0		1,290.0		1,128.7
Capital Expenditures
Portfolio investments and capital additions	(22.9)	(10.8)	$ (74.7)	(63.2)
ASC [Member]
Segment Reporting Information [Line Items]
Leverage level expressed as a ratio of recourse debt to equity			1.5
Profitability
Lease revenue	1.1	1.0	$ 3.1	3.1
Marine operating revenue	59.1	51.8	113.2	102.3
Other revenue	0.0	0.0	0.0	0.0
Total Revenues	60.2	52.8	116.3	105.4
Maintenance expense	7.7	6.1	14.6	12.3
Marine operating expense	34.7	31.5	70.6	64.0
Depreciation	4.0	4.2	8.1	8.6
Operating lease expense	0.3	2.0	1.5	4.0
Other operating expense	0.0	0.0	0.0	0.0
Total Expenses	46.7	43.8	94.8	88.9
Net gain on asset dispositions	0.0	0.0	0.0	0.0
Interest expense, net	(1.4)	1.1	(3.9)	3.3
Other (expense) income	0.0	(0.1)	0.8	(0.3)
Share of affiliates' earnings (pre-tax)	0.0	0.0	0.0	0.0
Segment profit (loss)	12.1	7.8	18.4	12.9
Disposition Gains on Owned Assets	0.0	0.0	0.0	0.0
Nonoperating Income, Residual Sharing Income	0.0	0.0	0.0	0.0
Nonremarketing Disposition Gain (Loss)	0.0	0.0	0.0	0.0
Asset Impairment Charges			0.0	0.0
Selected Balance Sheet Data
Investments in affiliated companies	0.0		0.0		0.0
Identifiable assets	310.1		310.1		278.8
Capital Expenditures
Portfolio investments and capital additions	(0.8)	0.0	$ (13.6)	(9.1)
Portfolio Management [Member]
Segment Reporting Information [Line Items]
Leverage level expressed as a ratio of recourse debt to equity			1
Profitability
Lease revenue	0.7	1.2	$ 3.1	4.6
Marine operating revenue	3.8	10.3	21.8	37.4
Other revenue	0.2	0.1	1.0	0.7
Total Revenues	4.7	11.6	25.9	42.7
Maintenance expense	0.0	0.0	0.0	0.0
Marine operating expense	4.2	7.7	19.2	24.9
Depreciation	1.7	1.7	5.2	5.2
Operating lease expense	0.0	0.0	0.0	0.0
Other operating expense	0.1	0.3	0.7	4.9
Total Expenses	6.0	9.7	25.1	35.0
Net gain on asset dispositions	0.3	49.1	11.1	84.9
Interest expense, net	(2.2)	2.1	(6.8)	6.4
Other (expense) income	0.0	0.0	2.3	0.0
Share of affiliates' earnings (pre-tax)	16.0	15.2	39.9	33.0
Segment profit (loss)	12.8	64.1	47.3	119.2
Disposition Gains on Owned Assets	0.0	(0.3)	1.8	4.2
Nonoperating Income, Residual Sharing Income	0.3	49.4	9.3	82.5
Nonremarketing Disposition Gain (Loss)	0.0	0.0	0.0	0.0
Asset Impairment Charges			0.0	1.8
Selected Balance Sheet Data
Investments in affiliated companies	439.5		439.5		375.3
Identifiable assets	616.8		616.8		593.5
Capital Expenditures
Portfolio investments and capital additions	(36.6)	0.0	(36.6)	0.0
Other [Member]
Profitability
Lease revenue	0.0	0.0	0.0	0.0
Marine operating revenue	0.0	0.0	0.0	0.0
Other revenue	0.0	0.0	0.0	0.0
Total Revenues	0.0	0.0	0.0	0.0
Maintenance expense	0.0	0.0	0.0	0.0
Marine operating expense	0.0	0.0	0.0	0.0
Depreciation	0.0	0.0	0.0	0.0
Operating lease expense	0.0	0.0	0.0	(0.1)
Other operating expense	0.0	0.0	0.0	0.0
Total Expenses	0.0	0.0	0.0	(0.1)
Net gain on asset dispositions	0.0	0.0	0.0	0.0
Interest expense, net	2.4	(1.4)	5.9	(2.9)
Other (expense) income	(1.5)	0.3	(1.2)	(0.8)
Share of affiliates' earnings (pre-tax)	0.0	0.0	0.0	0.0
Segment profit (loss)	0.9	1.7	4.7	2.2
Disposition Gains on Owned Assets	0.0	0.0	0.0	0.0
Nonoperating Income, Residual Sharing Income	0.0	0.0	0.0	0.0
Nonremarketing Disposition Gain (Loss)	0.0	0.0	0.0	0.0
Asset Impairment Charges			0.0	0.0
Selected Balance Sheet Data
Investments in affiliated companies	0.0		0.0		0.0
Identifiable assets	203.8		203.8		$ 328.8
Capital Expenditures
Portfolio investments and capital additions	(0.1)	(1.2)	(0.4)	(3.6)
Parent [Member]
Profitability
Income tax benefit	$ 24.3	$ 41.0	$ 69.9	$ 102.6