Financial Data of Business Segments (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($) Segment	Jun. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)
Segment Reporting Information [Line Items]
Provision for Income Taxes, Equity Method Investment	$ 2.7	$ 1.4	$ 5.7	$ 4.1
Number of business segments | Segment			4
Profitability
Lease revenue	274.1	281.2	$ 546.8	565.7
Marine operating revenue	55.1	57.3	72.1	77.6
Other revenue	19.2	20.4	45.6	50.0
Total Revenues	348.4	358.9	664.5	693.3
Maintenance expense	84.9	86.5	162.8	165.0
Marine operating expense	38.0	37.4	50.9	49.7
Depreciation	77.3	75.8	149.3	145.1
Operating lease expense	15.2	18.5	31.0	35.3
Other operating expense	7.8	14.8	17.4	23.6
Total Expenses	223.2	233.0	411.4	418.7
Net gain on asset dispositions	22.0	36.9	46.9	60.1
Interest expense, net	(40.0)	(36.5)	(79.2)	(73.7)
Other (expense) income	(1.1)	(3.9)	(2.4)	(7.2)
Share of affiliates' earnings (pre-tax)	12.4	7.8	24.1	18.0
Segment profit (loss)	118.5	130.2	242.5	271.8
SG&A	43.1	40.9	86.0	79.7
Income tax benefit	19.3	26.7	39.9	57.5
Net Income	53.4	61.2	110.9	130.5
Gain (Loss) on Sale of Assets and Asset Impairment Charges	22.0	36.9	46.9	60.1
Disposition Gains on Owned Assets	12.7	5.1	33.8	25.1
Nonoperating Income, Residual Sharing Income	8.9	31.7	9.3	33.5
Nonremarketing Disposition Gain (Loss)	2.3	1.9	5.7	3.3
Asset Impairment Charges	(1.9)	(1.8)	(1.9)	(1.8)
Selected Balance Sheet Data
Investments in affiliated companies	407.8		407.8		$ 387.0
Identifiable assets	7,272.1		7,272.1		7,105.4
Capital Expenditures
Portfolio investments and capital additions	(166.3)	(182.0)	$ (295.3)	(322.2)
Rail North America [Member]
Segment Reporting Information [Line Items]
Leverage level expressed as a ratio of recourse debt to equity			5
Profitability
Lease revenue	225.7	233.4	$ 452.9	470.0
Marine operating revenue	0.0	0.0	0.0	0.0
Other revenue	17.3	18.4	42.1	46.2
Total Revenues	243.0	251.8	495.0	516.2
Maintenance expense	68.5	67.6	136.2	133.4
Marine operating expense	0.0	0.0	0.0	0.0
Depreciation	59.7	58.1	118.7	114.6
Operating lease expense	14.8	16.6	29.8	33.4
Other operating expense	6.3	9.5	14.4	16.4
Total Expenses	149.3	151.8	299.1	297.8
Net gain on asset dispositions	10.7	4.7	34.5	23.3
Interest expense, net	(28.5)	(26.9)	(59.6)	(54.1)
Other (expense) income	(1.2)	(1.1)	(3.2)	(2.4)
Share of affiliates' earnings (pre-tax)	0.2	0.1	0.3	0.3
Segment profit (loss)	74.9	76.8	167.9	185.5
Disposition Gains on Owned Assets	10.9	3.0	32.0	20.6
Nonoperating Income, Residual Sharing Income	0.2	0.1	0.3	0.4
Nonremarketing Disposition Gain (Loss)	1.5	1.6	4.1	2.3
Asset Impairment Charges	(1.9)	0.0	(1.9)	0.0
Selected Balance Sheet Data
Investments in affiliated companies	10.5		10.5		10.5
Identifiable assets	4,834.4		4,834.4		4,775.6
Capital Expenditures
Portfolio investments and capital additions	(127.6)	(145.4)	$ (230.4)	(258.3)
Rail International [Member]
Segment Reporting Information [Line Items]
Leverage level expressed as a ratio of recourse debt to equity			3
Profitability
Lease revenue	46.2	45.3	$ 89.5	90.2
Marine operating revenue	0.0	0.0	0.0	0.0
Other revenue	1.6	1.6	2.7	3.2
Total Revenues	47.8	46.9	92.2	93.4
Maintenance expense	9.7	12.9	19.7	25.4
Marine operating expense	0.0	0.0	0.0	0.0
Depreciation	11.8	11.5	23.0	22.6
Operating lease expense	0.0	0.0	0.0	0.0
Other operating expense	1.2	1.2	2.4	2.6
Total Expenses	22.7	25.6	45.1	50.6
Net gain on asset dispositions	0.8	0.3	1.6	1.0
Interest expense, net	(8.1)	(7.3)	(16.0)	(14.6)
Other (expense) income	(1.1)	(1.3)	(2.6)	(3.5)
Share of affiliates' earnings (pre-tax)	(0.1)	0.0	(0.1)	(0.1)
Segment profit (loss)	16.6	13.0	30.0	25.6
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)	0.8	0.3	1.6	1.0
Asset Impairment Charges	0.0	0.0	0.0	0.0
Selected Balance Sheet Data
Investments in affiliated companies	1.2		1.2		1.2
Identifiable assets	1,246.3		1,246.3		1,128.7
Capital Expenditures
Portfolio investments and capital additions	(33.1)	(30.4)	$ (51.8)	(52.4)
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	1.1	$ 2.0	2.1
Marine operating revenue	47.7	46.4	54.1	50.5
Other revenue	0.0	0.0	0.0	0.0
Total Revenues	48.7	47.5	56.1	52.6
Maintenance expense	6.7	6.0	6.9	6.2
Marine operating expense	30.6	29.6	35.9	32.5
Depreciation	4.0	4.4	4.1	4.4
Operating lease expense	0.4	2.0	1.2	2.0
Other operating expense	0.0	0.0	0.0	0.0
Total Expenses	41.7	42.0	48.1	45.1
Net gain on asset dispositions	0.0	0.0	0.0	0.0
Interest expense, net	(1.3)	(1.1)	(2.5)	(2.2)
Other (expense) income	0.8	(0.2)	0.8	(0.2)
Share of affiliates' earnings (pre-tax)	0.0	0.0	0.0	0.0
Segment profit (loss)	6.5	4.2	6.3	5.1
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	0.0	0.0
Selected Balance Sheet Data
Investments in affiliated companies	0.0		0.0		0.0
Identifiable assets	321.6		321.6		278.8
Capital Expenditures
Portfolio investments and capital additions	(5.5)	(4.4)	$ (12.8)	(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	1.2	1.4	$ 2.4	3.4
Marine operating revenue	7.4	10.9	18.0	27.1
Other revenue	0.3	0.4	0.8	0.6
Total Revenues	8.9	12.7	21.2	31.1
Maintenance expense	0.0	0.0	0.0	0.0
Marine operating expense	7.4	7.8	15.0	17.2
Depreciation	1.8	1.8	3.5	3.5
Operating lease expense	0.0	0.0	0.0	0.0
Other operating expense	0.3	4.1	0.6	4.6
Total Expenses	9.5	13.7	19.1	25.3
Net gain on asset dispositions	10.5	31.9	10.8	35.8
Interest expense, net	(2.4)	(2.1)	(4.6)	(4.3)
Other (expense) income	0.0	0.0	2.3	0.0
Share of affiliates' earnings (pre-tax)	12.3	7.7	23.9	17.8
Segment profit (loss)	19.8	36.5	34.5	55.1
Disposition Gains on Owned Assets	1.8	2.1	1.8	4.5
Nonoperating Income, Residual Sharing Income	8.7	31.6	9.0	33.1
Nonremarketing Disposition Gain (Loss)	0.0	0.0	0.0	0.0
Asset Impairment Charges	0.0	(1.8)	0.0	(1.8)
Selected Balance Sheet Data
Investments in affiliated companies	396.1		396.1		375.3
Identifiable assets	595.5		595.5		593.5
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	(0.1)	0.0	(0.1)
Other operating expense	0.0	0.0	0.0	0.0
Total Expenses	0.0	(0.1)	0.0	(0.1)
Net gain on asset dispositions	0.0	0.0	0.0	0.0
Interest expense, net	0.3	0.9	3.5	1.5
Other (expense) income	0.4	(1.3)	0.3	(1.1)
Share of affiliates' earnings (pre-tax)	0.0	0.0	0.0	0.0
Segment profit (loss)	0.7	(0.3)	3.8	0.5
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	0.0	0.0
Selected Balance Sheet Data
Investments in affiliated companies	0.0		0.0		0.0
Identifiable assets	274.3		274.3		$ 328.8
Capital Expenditures
Portfolio investments and capital additions	(0.1)	(1.8)	(0.3)	(2.4)
Parent [Member]
Profitability
Income tax benefit	$ 22.0	$ 28.1	$ 45.6	$ 61.6