Financial Data of Business Segments (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) Segment	Jun. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2015
Segment Reporting Information [Line Items]
Provision for Income Taxes, Equity Method Investment	$ 0.0	$ 2.7
Number of business segments | Segment			4
Profitability
Lease revenue	271.0	274.1	$ 544.2	$ 546.8
Marine operating revenue	55.8	55.1	70.0	72.1
Other revenue	22.7	19.2	40.6	45.6
Total Revenues	349.5	348.4	654.8	664.5
Maintenance expense	82.0	84.9	163.2	162.8
Marine operating expense	37.6	38.0	50.1	50.9
Depreciation	81.1	77.3	158.5	149.3
Operating lease expense	12.7	15.2	25.7	31.0
Other operating expense	9.1	7.8	17.7	17.4
Total Expenses	222.5	223.2	415.2	411.4
Net gain on asset dispositions	6.1	22.0	62.2	46.9
Interest expense, net	(42.2)	(40.0)	(82.1)	(79.2)
Other (expense) income	(9.8)	(1.6)	(11.1)	(3.1)
Share of affiliates' earnings (pre-tax)	16.1	12.4	33.6	24.1
Segment profit (loss)	97.2	118.0	242.2	241.8
SG&A	46.2	42.6	91.1	85.3
Income tax benefit	9.1	19.3	29.7	39.9
Net Income	38.8	53.4	115.1	110.9
Disposition Gains on Owned Assets	4.2	12.7	54.2	33.8
Nonoperating Income, Residual Sharing Income	0.6	8.9	1.0	9.3
Nonremarketing Disposition Gain (Loss)	1.3	2.3	7.0	5.7
Asset Impairment Charges		(1.9)		(1.9)
Selected Balance Sheet Data
Investments in affiliated companies	468.9		468.9		$ 441.0
Identifiable assets	7,495.5		7,495.5		7,422.4
Capital Expenditures
Portfolio investments and capital additions	(188.6)	(166.3)	$ (367.0)	(295.3)
Rail North America [Member]
Segment Reporting Information [Line Items]
Leverage level expressed as a ratio of recourse debt to equity			5
Profitability
Lease revenue	217.6	225.7	$ 437.1	452.9
Marine operating revenue	0.0	0.0	0.0	0.0
Other revenue	20.1	17.3	35.9	42.1
Total Revenues	237.7	243.0	473.0	495.0
Maintenance expense	64.1	68.5	132.2	136.2
Marine operating expense	0.0	0.0	0.0	0.0
Depreciation	61.8	59.7	123.3	118.7
Operating lease expense	12.7	14.8	25.7	29.8
Other operating expense	7.5	6.3	14.4	14.4
Total Expenses	146.1	149.3	295.6	299.1
Net gain on asset dispositions	4.7	10.7	58.8	34.5
Interest expense, net	(31.1)	(28.5)	(61.3)	(59.6)
Other (expense) income	(1.2)	(1.2)	(2.1)	(3.2)
Share of affiliates' earnings (pre-tax)	0.2	0.2	0.3	0.3
Segment profit (loss)	64.2	74.9	173.1	167.9
Disposition Gains on Owned Assets	4.2	10.9	54.1	32.0
Nonoperating Income, Residual Sharing Income	0.3	0.2	0.4	0.3
Nonremarketing Disposition Gain (Loss)	0.2	1.5	4.3	4.1
Asset Impairment Charges		(1.9)		(1.9)
Selected Balance Sheet Data
Investments in affiliated companies	6.8		6.8		6.8
Identifiable assets	5,022.6		5,022.6		4,915.0
Capital Expenditures
Portfolio investments and capital additions	(149.1)	(127.6)	$ (285.6)	(230.4)
Rail International [Member]
Segment Reporting Information [Line Items]
Leverage level expressed as a ratio of recourse debt to equity			3
Profitability
Lease revenue	52.2	46.2	$ 104.6	89.5
Marine operating revenue	0.0	0.0	0.0	0.0
Other revenue	2.2	1.6	4.2	2.7
Total Revenues	54.4	47.8	108.8	92.2
Maintenance expense	11.2	9.7	23.7	19.7
Marine operating expense	0.0	0.0	0.0	0.0
Depreciation	13.8	11.8	27.9	23.0
Operating lease expense	0.0	0.0	0.0	0.0
Other operating expense	1.5	1.2	3.0	2.4
Total Expenses	26.5	22.7	54.6	45.1
Net gain on asset dispositions	1.1	0.8	2.7	1.6
Interest expense, net	(8.9)	(8.1)	(17.6)	(16.0)
Other (expense) income	(7.3)	(1.1)	(7.5)	(2.6)
Share of affiliates' earnings (pre-tax)	0.0	(0.1)	0.0	(0.1)
Segment profit (loss)	12.8	16.6	31.8	30.0
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)	1.1	0.8	2.7	1.6
Asset Impairment Charges		0.0		0.0
Selected Balance Sheet Data
Investments in affiliated companies	0.0		0.0		0.0
Identifiable assets	1,313.9		1,313.9		1,332.9
Capital Expenditures
Portfolio investments and capital additions	(34.6)	(33.1)	$ (64.1)	(51.8)
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	$ 2.0	2.0
Marine operating revenue	52.3	47.7	62.1	54.1
Other revenue	0.0	0.0	0.0	0.0
Total Revenues	53.3	48.7	64.1	56.1
Maintenance expense	6.7	6.7	7.3	6.9
Marine operating expense	33.4	30.6	41.6	35.9
Depreciation	3.6	4.0	3.6	4.1
Operating lease expense	0.0	0.4	0.0	1.2
Other operating expense	0.0	0.0	0.0	0.0
Total Expenses	43.7	41.7	52.5	48.1
Net gain on asset dispositions	0.0	0.0	0.1	0.0
Interest expense, net	(1.5)	(1.3)	(2.8)	(2.5)
Other (expense) income	(0.1)	0.8	(0.1)	0.8
Share of affiliates' earnings (pre-tax)	0.0	0.0	0.0	0.0
Segment profit (loss)	8.0	6.5	8.8	6.3
Disposition Gains on Owned Assets	0.0	0.0	0.1	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	313.6		313.6		286.7
Capital Expenditures
Portfolio investments and capital additions	(4.1)	(5.5)	$ (15.8)	(12.8)
Portfolio Management [Member]
Segment Reporting Information [Line Items]
Leverage level expressed as a ratio of recourse debt to equity			1
Profitability
Lease revenue	0.2	1.2	$ 0.5	2.4
Marine operating revenue	3.5	7.4	7.9	18.0
Other revenue	0.4	0.3	0.5	0.8
Total Revenues	4.1	8.9	8.9	21.2
Maintenance expense	0.0	0.0	0.0	0.0
Marine operating expense	4.2	7.4	8.5	15.0
Depreciation	1.9	1.8	3.7	3.5
Operating lease expense	0.0	0.0	0.0	0.0
Other operating expense	0.1	0.3	0.3	0.6
Total Expenses	6.2	9.5	12.5	19.1
Net gain on asset dispositions	0.3	10.5	0.6	10.8
Interest expense, net	(2.7)	(2.4)	(5.0)	(4.6)
Other (expense) income	0.0	0.0	0.0	2.3
Share of affiliates' earnings (pre-tax)	15.9	12.3	33.3	23.9
Segment profit (loss)	11.4	19.8	25.3	34.5
Disposition Gains on Owned Assets	0.0	1.8	0.0	1.8
Nonoperating Income, Residual Sharing Income	0.3	8.7	0.6	9.0
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	462.1		462.1		434.2
Identifiable assets	606.0		606.0		582.8
Capital Expenditures
Portfolio investments and capital additions	0.0	0.0	0.0	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	0.0
Other operating expense	0.0	0.0	0.0	0.0
Total Expenses	0.0	0.0	0.0	0.0
Net gain on asset dispositions	0.0	0.0	0.0	0.0
Interest expense, net	2.0	0.3	4.6	3.5
Other (expense) income	(1.2)	(0.1)	(1.4)	(0.4)
Share of affiliates' earnings (pre-tax)	0.0	0.0	0.0	0.0
Segment profit (loss)	0.8	0.2	3.2	3.1
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	239.4		239.4		$ 305.0
Capital Expenditures
Portfolio investments and capital additions	(0.8)	(0.1)	(1.5)	(0.3)
Parent [Member]
Profitability
Income tax benefit	$ 12.2	$ 22.0	$ 36.0	$ 45.6
Cardinal Marine [Domain]
Capital Expenditures
Noncontrolling Interest, Ownership Percentage by Parent						50.00%