Financial Data of Business Segments (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) Segment	Jun. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)
Segment Reporting Information [Line Items]
Provision for Income Taxes, Equity Method Investment	$ 3.5	$ 3.1	$ 7.0	$ 6.3
Number of business segments | Segment			4
Profitability
Lease revenue	274.0	271.0	$ 548.4	544.2
Other revenue	24.5	22.7	54.0	40.6
Total Revenues	359.4	349.5	676.4	654.8
Maintenance expense	85.7	82.0	166.9	163.2
Marine operating expense	41.0	37.6	53.1	50.1
Depreciation	83.8	81.1	163.7	158.5
Operating lease expense	13.7	12.7	27.4	25.7
Other operating expense	7.8	9.1	15.8	17.7
Total Expenses	232.0	222.5	426.9	415.2
Net gain on asset dispositions	32.9	6.1	41.8	62.2
Interest expense, net	(47.1)	(42.2)	(93.6)	(82.1)
Other (expense) income	(0.6)	(9.8)	(3.8)	(11.1)
Share of affiliates' earnings (pre-tax)	19.6	16.1	37.8	33.6
Segment profit (loss)	132.2	97.2	231.7	242.2
SG&A	45.1	46.2	91.2	91.1
Income tax benefit	15.6	9.1	24.0	29.7
Net Income	68.0	38.8	109.5	115.1
Disposition Gains on Owned Assets	26.8	4.2	36.5	54.2
Nonoperating Income, Residual Sharing Income	0.4	0.6	0.8	1.0
Nonremarketing Disposition Gain (Loss)	5.7	1.3	4.5	7.0
Selected Balance Sheet Data
Investments in affiliated companies	495.8		495.8		$ 464.5
Identifiable assets	8,353.1		8,353.1		7,616.7
Capital Expenditures
Portfolio investments and capital additions	(184.1)	(188.6)	(331.4)	(367.0)
Revenue Recognition, Cargo and Freight, Policy [Policy Text Block]	60.9	55.8	74.0	70.0
Rail North America [Member]
Profitability
Lease revenue	218.8	217.6	439.7	437.1
Other revenue	22.4	20.1	49.8	35.9
Total Revenues	241.2	237.7	489.5	473.0
Maintenance expense	67.0	64.1	135.8	132.2
Marine operating expense	0.0	0.0	0.0	0.0
Depreciation	64.4	61.8	128.7	123.3
Operating lease expense	13.7	12.7	27.4	25.7
Other operating expense	6.4	7.5	12.8	14.4
Total Expenses	151.5	146.1	304.7	295.6
Net gain on asset dispositions	32.1	4.7	40.3	58.8
Interest expense, net	(34.1)	31.1	(68.3)	(61.3)
Other (expense) income	(1.9)	(1.2)	(2.6)	(2.1)
Share of affiliates' earnings (pre-tax)	0.0	0.2	0.0	0.3
Segment profit (loss)	85.8	64.2	154.2	173.1
Disposition Gains on Owned Assets	26.8	4.2	36.5	54.1
Nonoperating Income, Residual Sharing Income	0.1	0.3	0.2	0.4
Nonremarketing Disposition Gain (Loss)	5.2	0.2	3.6	4.3
Selected Balance Sheet Data
Investments in affiliated companies	0.2		0.2		0.2
Identifiable assets	5,618.8		5,618.8		5,236.6
Capital Expenditures
Portfolio investments and capital additions	(105.3)	(149.1)	(204.3)	(285.6)
Revenue Recognition, Cargo and Freight, Policy [Policy Text Block]	0.0	0.0	0.0	0.0
Rail International [Member]
Profitability
Lease revenue	53.9	52.2	106.1	104.6
Other revenue	1.8	2.2	3.8	4.2
Total Revenues	55.7	54.4	109.9	108.8
Maintenance expense	11.2	11.2	23.3	23.7
Marine operating expense	0.0	0.0	0.0	0.0
Depreciation	14.2	13.8	28.2	27.9
Operating lease expense	0.0	0.0	0.0	0.0
Other operating expense	1.3	1.5	2.8	3.0
Total Expenses	26.7	26.5	54.3	54.6
Net gain on asset dispositions	0.5	1.1	0.9	2.7
Interest expense, net	(10.1)	(8.9)	(20.0)	(17.6)
Other (expense) income	1.9	(7.3)	(0.4)	(7.5)
Share of affiliates' earnings (pre-tax)	0.0	0.0	0.0	0.0
Segment profit (loss)	21.3	12.8	36.1	31.8
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)	0.5	1.1	0.9	2.7
Selected Balance Sheet Data
Investments in affiliated companies	0.0		0.0		0.0
Identifiable assets	1,440.2		1,440.2		1,363.2
Capital Expenditures
Portfolio investments and capital additions	(73.7)	(34.6)	(106.8)	(64.1)
Revenue Recognition, Cargo and Freight, Policy [Policy Text Block]	0.0	0.0	0.0	0.0
ASC [Member]
Profitability
Lease revenue	1.1	1.0	2.1	2.0
Other revenue	0.0	0.0	0.0	0.0
Total Revenues	61.9	53.3	73.6	64.1
Maintenance expense	7.5	6.7	7.8	7.3
Marine operating expense	37.0	33.4	44.5	41.6
Depreciation	3.5	3.6	3.5	3.6
Operating lease expense	0.0	0.0	0.0	0.0
Other operating expense	0.0	0.0	0.0	0.0
Total Expenses	48.0	43.7	55.8	52.5
Net gain on asset dispositions	0.0	0.0	0.0	0.1
Interest expense, net	(1.6)	1.5	(3.0)	(2.8)
Other (expense) income	(0.2)	(0.1)	(0.2)	(0.1)
Share of affiliates' earnings (pre-tax)	0.0	0.0	0.0	0.0
Segment profit (loss)	12.1	8.0	14.6	8.8
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	331.3		331.3		297.8
Capital Expenditures
Portfolio investments and capital additions	(3.9)	(4.1)	(18.4)	(15.8)
Revenue Recognition, Cargo and Freight, Policy [Policy Text Block]	60.8	52.3	71.5	62.1
Portfolio Management [Member]
Profitability
Lease revenue	0.2	0.2	0.5	0.5
Other revenue	0.3	0.4	0.4	0.5
Total Revenues	0.6	4.1	3.4	8.9
Maintenance expense	0.0	0.0	0.0	0.0
Marine operating expense	4.0	4.2	8.6	8.5
Depreciation	1.7	1.9	3.3	3.7
Operating lease expense	0.0	0.0	0.0	0.0
Other operating expense	0.1	0.1	0.2	0.3
Total Expenses	5.8	6.2	12.1	12.5
Net gain on asset dispositions	0.3	0.3	0.6	0.6
Interest expense, net	(2.8)	2.7	(5.5)	(5.0)
Other (expense) income	0.0	0.0	0.0	0.0
Share of affiliates' earnings (pre-tax)	19.6	15.9	37.8	33.3
Segment profit (loss)	11.9	11.4	24.2	25.3
Disposition Gains on Owned Assets	0.0	0.0	0.0	0.0
Nonoperating Income, Residual Sharing Income	0.3	0.3	0.6	0.6
Nonremarketing Disposition Gain (Loss)	0.0	0.0	0.0	0.0
Selected Balance Sheet Data
Investments in affiliated companies	495.6		495.6		464.3
Identifiable assets	628.8		628.8		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]	0.1	3.5	2.5	7.9
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	1.5	(2.0)	3.2	4.6
Other (expense) income	(0.4)	(1.2)	(0.6)	(1.4)
Share of affiliates' earnings (pre-tax)	0.0	0.0	0.0	0.0
Segment profit (loss)	1.1	0.8	2.6	3.2
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
Selected Balance Sheet Data
Investments in affiliated companies	0.0		0.0		0.0
Identifiable assets	334.0		334.0		$ 112.3
Capital Expenditures
Portfolio investments and capital additions	(1.2)	(0.8)	(1.9)	(1.5)
Revenue Recognition, Cargo and Freight, Policy [Policy Text Block]	0.0	0.0	0.0	0.0
Parent [Member]
Profitability
Income tax benefit	$ 19.1	$ 12.2	$ 31.0	$ 36.0