Financial Data of Business Segments (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) Segment	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2015
Segment Reporting Information [Line Items]
Provision for Income Taxes, Equity Method Investment	$ 2.7	$ 3.9	$ 9.0	$ 9.6
Number of business segments | Segment			4
Profitability
Lease revenue	271.9	276.6	$ 816.1	823.4
Other revenue	17.0	20.1	57.6	65.7
Total Revenues	349.7	359.6	1,004.5	1,024.1
Maintenance expense	77.5	84.9	240.7	247.7
Marine operating expense	39.4	38.9	89.5	89.8
Depreciation	81.6	78.6	240.1	227.9
Operating lease expense	11.8	15.8	37.5	46.8
Other operating expense	8.5	8.5	26.2	25.9
Total Expenses	218.8	226.7	634.0	638.1
Net gain on asset dispositions	10.3	9.4	72.5	56.3
Interest expense, net	(42.6)	(40.2)	(124.7)	(119.4)
Other (expense) income	(3.8)	(2.4)	(14.9)	(5.5)
Share of affiliates' earnings (pre-tax)	14.5	16.1	48.1	40.2
Segment profit (loss)	109.3	115.8	351.5	357.6
SG&A	46.5	42.5	137.6	127.8
Income tax benefit	13.1	20.4	42.8	60.3
Net Income	47.0	49.0	162.1	159.9
Disposition Gains on Owned Assets	6.7	7.6	60.9	41.4
Nonoperating Income, Residual Sharing Income	0.7	0.5	1.7	9.8
Nonremarketing Disposition Gain (Loss)	2.9	1.3	9.9	7.0
Asset Impairment Charges				(1.9)
Selected Balance Sheet Data
Investments in affiliated companies	478.5		478.5		$ 441.0
Identifiable assets	7,517.4		7,517.4		7,422.4
Capital Expenditures
Portfolio investments and capital additions	(169.7)	(163.7)	(536.7)	(459.0)
Revenue Recognition, Cargo and Freight, Policy [Policy Text Block]	60.8	62.9	$ 130.8	135.0
Rail North America [Member]
Segment Reporting Information [Line Items]
Leverage level expressed as a ratio of recourse debt to equity			5
Profitability
Lease revenue	218.2	224.5	$ 655.3	677.4
Other revenue	15.2	17.9	51.1	60.0
Total Revenues	233.4	242.4	706.4	737.4
Maintenance expense	60.6	66.1	192.8	202.3
Marine operating expense	0.0	0.0	0.0	0.0
Depreciation	62.5	60.1	185.8	178.8
Operating lease expense	11.8	15.5	37.5	45.3
Other operating expense	7.1	7.3	21.5	21.7
Total Expenses	142.0	149.0	437.6	448.1
Net gain on asset dispositions	9.6	8.1	68.4	42.6
Interest expense, net	(31.8)	(30.5)	(93.1)	(90.1)
Other (expense) income	(1.2)	(0.9)	(3.3)	(4.1)
Share of affiliates' earnings (pre-tax)	0.2	0.1	0.5	0.4
Segment profit (loss)	68.2	70.2	241.3	238.1
Disposition Gains on Owned Assets	6.7	7.5	60.8	39.5
Nonoperating Income, Residual Sharing Income	0.5	0.2	0.9	0.5
Nonremarketing Disposition Gain (Loss)	2.4	0.4	6.7	4.5
Asset Impairment Charges				(1.9)
Selected Balance Sheet Data
Investments in affiliated companies	3.7		3.7		6.8
Identifiable assets	5,000.0		5,000.0		4,915.0
Capital Expenditures
Portfolio investments and capital additions	(129.1)	(103.3)	(414.7)	(333.7)
Revenue Recognition, Cargo and Freight, Policy [Policy Text Block]	0.0	0.0	$ 0.0	0.0
Rail International [Member]
Segment Reporting Information [Line Items]
Leverage level expressed as a ratio of recourse debt to equity			3
Profitability
Lease revenue	52.3	50.3	$ 156.9	139.8
Other revenue	1.8	2.0	6.0	4.7
Total Revenues	54.1	52.3	162.9	144.5
Maintenance expense	10.1	11.1	33.8	30.8
Marine operating expense	0.0	0.0	0.0	0.0
Depreciation	13.8	12.8	41.7	35.8
Operating lease expense	0.0	0.0	0.0	0.0
Other operating expense	1.3	1.1	4.3	3.5
Total Expenses	25.2	25.0	79.8	70.1
Net gain on asset dispositions	0.5	1.0	3.2	2.6
Interest expense, net	(8.9)	(8.5)	(26.5)	(24.5)
Other (expense) income	0.2	0.3	(7.3)	(2.3)
Share of affiliates' earnings (pre-tax)	0.0	0.0	0.0	(0.1)
Segment profit (loss)	20.7	20.1	52.5	50.1
Disposition Gains on Owned Assets	0.0	0.1	0.0	0.1
Nonoperating Income, Residual Sharing Income	0.0	0.0	0.0	0.0
Nonremarketing Disposition Gain (Loss)	0.5	0.9	3.2	2.5
Asset Impairment Charges				0.0
Selected Balance Sheet Data
Investments in affiliated companies	0.0		0.0		0.0
Identifiable assets	1,357.3		1,357.3		1,332.9
Capital Expenditures
Portfolio investments and capital additions	(40.4)	(22.9)	(104.5)	(74.7)
Revenue Recognition, Cargo and Freight, Policy [Policy Text Block]	0.0	0.0	$ 0.0	0.0
ASC [Member]
Segment Reporting Information [Line Items]
Leverage level expressed as a ratio of recourse debt to equity			1.5
Profitability
Lease revenue	1.1	1.1	$ 3.1	3.1
Other revenue	0.0	0.0	0.0	0.0
Total Revenues	58.8	60.2	122.9	116.3
Maintenance expense	6.8	7.7	14.1	14.6
Marine operating expense	35.0	34.7	76.6	70.6
Depreciation	3.5	4.0	7.1	8.1
Operating lease expense	0.0	0.3	0.0	1.5
Other operating expense	0.0	0.0	0.0	0.0
Total Expenses	45.3	46.7	97.8	94.8
Net gain on asset dispositions	0.0	0.0	0.1	0.0
Interest expense, net	(1.5)	(1.4)	(4.3)	(3.9)
Other (expense) income	(0.1)	0.0	(0.2)	0.8
Share of affiliates' earnings (pre-tax)	0.0	0.0	0.0	0.0
Segment profit (loss)	11.9	12.1	20.7	18.4
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
Selected Balance Sheet Data
Investments in affiliated companies	0.0		0.0		0.0
Identifiable assets	303.5		303.5		286.7
Capital Expenditures
Portfolio investments and capital additions	0.0	(0.8)	(15.8)	(13.6)
Revenue Recognition, Cargo and Freight, Policy [Policy Text Block]	57.7	59.1	$ 119.8	113.2
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	0.7	$ 0.8	3.1
Other revenue	0.0	0.2	0.5	1.0
Total Revenues	3.4	4.7	12.3	25.9
Maintenance expense	0.0	0.0	0.0	0.0
Marine operating expense	4.4	4.2	12.9	19.2
Depreciation	1.8	1.7	5.5	5.2
Operating lease expense	0.0	0.0	0.0	0.0
Other operating expense	0.1	0.1	0.4	0.7
Total Expenses	6.3	6.0	18.8	25.1
Net gain on asset dispositions	0.2	0.3	0.8	11.1
Interest expense, net	(2.6)	(2.2)	(7.6)	(6.8)
Other (expense) income	0.0	0.0	0.0	2.3
Share of affiliates' earnings (pre-tax)	14.3	16.0	47.6	39.9
Segment profit (loss)	9.0	12.8	34.3	47.3
Disposition Gains on Owned Assets	0.0	0.0	0.0	1.8
Nonoperating Income, Residual Sharing Income	0.2	0.3	0.8	9.3
Nonremarketing Disposition Gain (Loss)	0.0	0.0	0.0	0.0
Asset Impairment Charges				0.0
Selected Balance Sheet Data
Investments in affiliated companies	474.8		474.8		434.2
Identifiable assets	614.9		614.9		582.8
Capital Expenditures
Portfolio investments and capital additions	0.0	(36.6)	0.0	(36.6)
Revenue Recognition, Cargo and Freight, Policy [Policy Text Block]	3.1	3.8	11.0	21.8
Other [Member]
Profitability
Lease 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	2.2	2.4	6.8	5.9
Other (expense) income	(2.7)	(1.8)	(4.1)	(2.2)
Share of affiliates' earnings (pre-tax)	0.0	0.0	0.0	0.0
Segment profit (loss)	(0.5)	0.6	2.7	3.7
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
Selected Balance Sheet Data
Investments in affiliated companies	0.0		0.0		0.0
Identifiable assets	241.7		241.7		$ 305.0
Capital Expenditures
Portfolio investments and capital additions	(0.2)	(0.1)	(1.7)	(0.4)
Revenue Recognition, Cargo and Freight, Policy [Policy Text Block]	0.0	0.0	0.0	0.0
Parent [Member]
Profitability
Income tax benefit	$ 15.8	$ 24.3	$ 51.8	$ 69.9
Cardinal Marine [Domain]
Capital Expenditures
Noncontrolling Interest, Ownership Percentage by Parent						50.00%