Financial Data of Business Segments (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) Segment	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)
Segment Reporting Information [Line Items]
Provision for Income Taxes, Equity Method Investment		$ 2.7		$ 9.0
Number of business segments | Segment			4
Profitability
Lease revenue	$ 271.5	271.9	$ 819.9	816.1
Other revenue	26.4	17.0	80.4	57.6
Total Revenues	360.7	349.7	1,037.1	1,004.5
Maintenance expense	84.4	77.5	251.3	240.7
Marine operating expense	39.7	39.4	92.8	89.5
Depreciation	83.6	81.6	247.3	240.1
Operating lease expense	13.7	11.8	41.1	37.5
Other operating expense	7.7	8.5	23.5	26.2
Total Expenses	229.1	218.8	656.0	634.0
Net gain on asset dispositions	5.1	10.3	46.9	72.5
Interest expense, net	(46.3)	(42.6)	(139.9)	(124.7)
Other (expense) income	(1.8)	(3.8)	(5.6)	(14.9)
Share of affiliates' earnings (pre-tax)	15.8	14.5	53.6	48.1
Segment profit (loss)	104.4	109.3	336.1	351.5
SG&A	44.4	46.5	135.6	137.6
Income tax benefit	11.9	13.1	35.9	42.8
Net Income	45.1	47.0	154.6	162.1
Disposition Gains on Owned Assets	4.4	6.7	40.9	60.9
Nonoperating Income, Residual Sharing Income	0.6	0.7	1.4	1.7
Nonremarketing Disposition Gain (Loss)	0.1	2.9	4.6	9.9
Selected Balance Sheet Data
Investments in affiliated companies	506.7		506.7		$ 464.5
Identifiable assets	8,090.9		8,090.9		7,616.7
Capital Expenditures
Portfolio investments and capital additions	(191.1)	(169.7)	(522.5)	(536.7)
Revenue Recognition, Cargo and Freight, Policy [Policy Text Block]	62.8	60.8	136.8	130.8
Rail North America [Member]
Profitability
Lease revenue	214.6	218.2	654.3	655.3
Other revenue	23.9	15.2	73.7	51.1
Total Revenues	238.5	233.4	728.0	706.4
Maintenance expense	64.0	60.6	199.8	192.8
Marine operating expense	0.0	0.0	0.0	0.0
Depreciation	63.9	62.5	192.6	185.8
Operating lease expense	13.7	11.8	41.1	37.5
Other operating expense	6.2	7.1	19.0	21.5
Total Expenses	147.8	142.0	452.5	437.6
Net gain on asset dispositions	4.3	9.6	44.6	68.4
Interest expense, net	(33.1)	31.8	(101.4)	(93.1)
Other (expense) income	(1.0)	(1.2)	(3.6)	(3.3)
Share of affiliates' earnings (pre-tax)	0.0	0.2	0.0	0.5
Segment profit (loss)	60.9	68.2	215.1	241.3
Disposition Gains on Owned Assets	4.4	6.7	40.9	60.8
Nonoperating Income, Residual Sharing Income	0.1	0.5	0.3	0.9
Nonremarketing Disposition Gain (Loss)	(0.2)	2.4	3.4	6.7
Selected Balance Sheet Data
Investments in affiliated companies	0.2		0.2		0.2
Identifiable assets	5,625.5		5,625.5		5,236.6
Capital Expenditures
Portfolio investments and capital additions	(138.1)	(129.1)	(342.4)	(414.7)
Revenue Recognition, Cargo and Freight, Policy [Policy Text Block]	0.0	0.0	0.0	0.0
Rail International [Member]
Profitability
Lease revenue	55.6	52.3	161.7	156.9
Other revenue	2.4	1.8	6.2	6.0
Total Revenues	58.0	54.1	167.9	162.9
Maintenance expense	12.2	10.1	35.5	33.8
Marine operating expense	0.0	0.0	0.0	0.0
Depreciation	14.5	13.8	42.7	41.7
Operating lease expense	0.0	0.0	0.0	0.0
Other operating expense	1.4	1.3	4.2	4.3
Total Expenses	28.1	25.2	82.4	79.8
Net gain on asset dispositions	0.3	0.5	1.2	3.2
Interest expense, net	(10.2)	(8.9)	(30.2)	(26.5)
Other (expense) income	(0.1)	0.2	(0.5)	(7.3)
Share of affiliates' earnings (pre-tax)	0.0	0.0	0.0	0.0
Segment profit (loss)	19.9	20.7	56.0	52.5
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)	0.3	0.5	1.2	3.2
Selected Balance Sheet Data
Investments in affiliated companies	0.0		0.0		0.0
Identifiable assets	1,397.2		1,397.2		1,363.2
Capital Expenditures
Portfolio investments and capital additions	(51.8)	(40.4)	(158.6)	(104.5)
Revenue Recognition, Cargo and Freight, Policy [Policy Text Block]	0.0	0.0	0.0	0.0
ASC [Member]
Profitability
Lease revenue	1.0	1.1	3.1	3.1
Other revenue	0.0	0.0	0.0	0.0
Total Revenues	61.9	58.8	135.5	122.9
Maintenance expense	8.2	6.8	16.0	14.1
Marine operating expense	36.3	35.0	80.8	76.6
Depreciation	3.6	3.5	7.1	7.1
Operating lease expense	0.0	0.0	0.0	0.0
Other operating expense	0.0	0.0	0.0	0.0
Total Expenses	48.1	45.3	103.9	97.8
Net gain on asset dispositions	0.0	0.0	0.0	0.1
Interest expense, net	(1.6)	1.5	(4.6)	(4.3)
Other (expense) income	(0.1)	(0.1)	(0.3)	(0.2)
Share of affiliates' earnings (pre-tax)	0.0	0.0	0.0	0.0
Segment profit (loss)	12.1	11.9	26.7	20.7
Disposition Gains on Owned Assets	0.0	0.0	0.0	0.1
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
Selected Balance Sheet Data
Investments in affiliated companies	0.0		0.0		0.0
Identifiable assets	319.1		319.1		297.8
Capital Expenditures
Portfolio investments and capital additions	(0.3)	0.0	(18.7)	(15.8)
Revenue Recognition, Cargo and Freight, Policy [Policy Text Block]	60.9	57.7	132.4	119.8
Portfolio Management [Member]
Profitability
Lease revenue	0.3	0.3	0.8	0.8
Other revenue	0.1	0.0	0.5	0.5
Total Revenues	2.3	3.4	5.7	12.3
Maintenance expense	0.0	0.0	0.0	0.0
Marine operating expense	3.4	4.4	12.0	12.9
Depreciation	1.6	1.8	4.9	5.5
Operating lease expense	0.0	0.0	0.0	0.0
Other operating expense	0.1	0.1	0.3	0.4
Total Expenses	5.1	6.3	17.2	18.8
Net gain on asset dispositions	0.5	0.2	1.1	0.8
Interest expense, net	(2.8)	2.6	(8.3)	(7.6)
Other (expense) income	0.0	0.0	0.0	0.0
Share of affiliates' earnings (pre-tax)	15.8	14.3	53.6	47.6
Segment profit (loss)	10.7	9.0	34.9	34.3
Disposition Gains on Owned Assets	0.0	0.0	0.0	0.0
Nonoperating Income, Residual Sharing Income	0.5	0.2	1.1	0.8
Nonremarketing Disposition Gain (Loss)	0.0	0.0	0.0	0.0
Selected Balance Sheet Data
Investments in affiliated companies	506.5		506.5		464.3
Identifiable assets	639.6		639.6		606.8
Capital Expenditures
Portfolio investments and capital additions	0.0	0.0	0.0	0.0
Revenue Recognition, Cargo and Freight, Policy [Policy Text Block]	1.9	3.1	4.4	11.0
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	1.4	(2.2)	4.6	6.8
Other (expense) income	(0.6)	(2.7)	(1.2)	(4.1)
Share of affiliates' earnings (pre-tax)	0.0	0.0	0.0	0.0
Segment profit (loss)	0.8	(0.5)	3.4	2.7
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
Selected Balance Sheet Data
Investments in affiliated companies	0.0		0.0		0.0
Identifiable assets	109.5		109.5		$ 112.3
Capital Expenditures
Portfolio investments and capital additions	(0.9)	(0.2)	(2.8)	(1.7)
Revenue Recognition, Cargo and Freight, Policy [Policy Text Block]	0.0	0.0	0.0	0.0
Parent [Member]
Profitability
Income tax benefit	$ 14.9	$ 15.8	$ 45.9	$ 51.8