Financial Data of Business Segments (Details) $ in Millions	3 Months Ended
	Mar. 31, 2020 USD ($) Segment AircraftEngines	Mar. 31, 2019 USD ($)	Dec. 31, 2019 USD ($)
Segment Reporting Information [Line Items]
Number of business segments | Segment	4
Profitability
Lease revenue	$ 271.7	$ 274.4
Other revenue	25.4	29.5
Total Revenues	308.9	317.0
Maintenance expense	86.6	81.2
Marine operating expense	10.4	12.1
Depreciation	80.4	79.9
Operating lease expense	13.3	13.7
Other operating expense	8.5	8.0
Total Expenses	199.2	194.9
Net gain on asset dispositions	27.4	8.9
Interest expense, net	(46.8)	(46.5)
Other (expense) income	(8.2)	(3.2)
Share of affiliates' earnings (pre-tax)	23.8	18.2
Segment profit (loss)	105.9	99.5
SG&A	42.4	46.1
Income tax benefit	12.9	8.4
Net Income	46.3	41.5
Disposition Gains on Owned Assets	26.9	9.7
Nonoperating Income, Residual Sharing Income	0.6	0.4
Nonremarketing Disposition Gain (Loss)	(0.1)	(1.2)
Selected Balance Sheet Data
Investments in affiliated companies	532.4		$ 512.6
Identifiable assets	8,717.9		8,285.1
Capital Expenditures
Portfolio investments and capital additions	(194.7)	(147.3)
Revenue Recognition, Cargo and Freight, Policy [Policy Text Block]	11.8	13.1
Rail North America [Member]
Profitability
Lease revenue	212.1	220.9
Other revenue	23.6	27.4
Total Revenues	235.7	248.3
Maintenance expense	72.9	68.8
Marine operating expense	0.0	0.0
Depreciation	63.6	64.3
Operating lease expense	13.3	13.7
Other operating expense	6.6	6.4
Total Expenses	156.4	153.2
Net gain on asset dispositions	26.8	8.2
Interest expense, net	(33.3)	(34.2)
Other (expense) income	(0.8)	(0.7)
Share of affiliates' earnings (pre-tax)	0.0	0.0
Segment profit (loss)	72.0	68.4
Disposition Gains on Owned Assets	26.9	9.7
Nonoperating Income, Residual Sharing Income	0.1	0.1
Nonremarketing Disposition Gain (Loss)	(0.2)	(1.6)
Selected Balance Sheet Data
Investments in affiliated companies	0.2		0.2
Identifiable assets	5,679.0		5,646.7
Capital Expenditures
Portfolio investments and capital additions	(110.9)	(99.0)
Revenue Recognition, Cargo and Freight, Policy [Policy Text Block]	0.0	0.0
Rail International [Member]
Profitability
Lease revenue	58.3	52.2
Other revenue	1.8	2.0
Total Revenues	60.1	54.2
Maintenance expense	12.9	12.1
Marine operating expense	0.0	0.0
Depreciation	15.5	14.0
Operating lease expense	0.0	0.0
Other operating expense	1.8	1.5
Total Expenses	30.2	27.6
Net gain on asset dispositions	0.1	0.4
Interest expense, net	(10.6)	(9.9)
Other (expense) income	(5.5)	(2.3)
Share of affiliates' earnings (pre-tax)	0.0	0.0
Segment profit (loss)	13.9	14.8
Disposition Gains on Owned Assets	0.0	0.0
Nonoperating Income, Residual Sharing Income	0.0	0.0
Nonremarketing Disposition Gain (Loss)	0.1	0.4
Selected Balance Sheet Data
Investments in affiliated companies	0.0		0.0
Identifiable assets	1,497.4		1,486.7
Capital Expenditures
Portfolio investments and capital additions	(69.3)	(33.1)
Revenue Recognition, Cargo and Freight, Policy [Policy Text Block]	0.0	0.0
ASC [Member]
Profitability
Lease revenue	1.0	1.0
Other revenue	0.0	0.0
Total Revenues	9.5	11.7
Maintenance expense	0.8	0.3
Marine operating expense	6.3	7.5
Depreciation	0.0	0.0
Operating lease expense	0.0	0.0
Other operating expense	0.0	0.0
Total Expenses	7.1	7.8
Net gain on asset dispositions	0.0	0.0
Interest expense, net	(1.3)	(1.4)
Other (expense) income	(0.2)	0.0
Share of affiliates' earnings (pre-tax)	0.0	0.0
Segment profit (loss)	0.9	2.5
Disposition Gains on Owned Assets	0.0	0.0
Nonoperating Income, Residual Sharing Income	0.0	0.0
Nonremarketing Disposition Gain (Loss)	0.0	0.0
Selected Balance Sheet Data
Investments in affiliated companies	0.0		0.0
Identifiable assets	300.9		291.1
Capital Expenditures
Portfolio investments and capital additions	(13.7)	(14.5)
Revenue Recognition, Cargo and Freight, Policy [Policy Text Block]	8.5	10.7
Portfolio Management [Member]
Profitability
Lease revenue	0.3	0.3
Other revenue	0.0	0.1
Total Revenues	3.6	2.8
Maintenance expense	0.0	0.0
Marine operating expense	4.1	4.6
Depreciation	1.3	1.6
Operating lease expense	0.0	0.0
Other operating expense	0.1	0.1
Total Expenses	5.5	6.3
Net gain on asset dispositions	0.5	0.3
Interest expense, net	(2.9)	(2.7)
Other (expense) income	0.0	0.0
Share of affiliates' earnings (pre-tax)	23.8	18.2
Segment profit (loss)	19.5	12.3
Disposition Gains on Owned Assets	0.0	0.0
Nonoperating Income, Residual Sharing Income	0.5	0.3
Nonremarketing Disposition Gain (Loss)	0.0	0.0
Selected Balance Sheet Data
Investments in affiliated companies	532.2		512.4
Identifiable assets	657.3		653.7
Capital Expenditures
Portfolio investments and capital additions	(0.3)	0.0
Revenue Recognition, Cargo and Freight, Policy [Policy Text Block]	$ 3.3	2.4
Number of Specialized Gas Vessels | AircraftEngines	5
Other [Member]
Profitability
Lease revenue	$ 0.0	0.0
Other revenue	0.0	0.0
Total Revenues	0.0	0.0
Maintenance expense	0.0	0.0
Marine operating expense	0.0	0.0
Depreciation	0.0	0.0
Operating lease expense	0.0	0.0
Other operating expense	0.0	0.0
Total Expenses	0.0	0.0
Net gain on asset dispositions	0.0	0.0
Interest expense, net	1.3	1.7
Other (expense) income	(1.7)	(0.2)
Share of affiliates' earnings (pre-tax)	0.0	0.0
Segment profit (loss)	(0.4)	1.5
Disposition Gains on Owned Assets	0.0	0.0
Nonoperating Income, Residual Sharing Income	0.0	0.0
Nonremarketing Disposition Gain (Loss)	0.0	0.0
Selected Balance Sheet Data
Investments in affiliated companies	0.0		0.0
Identifiable assets	583.3		$ 206.9
Capital Expenditures
Portfolio investments and capital additions	(0.5)	(0.7)
Revenue Recognition, Cargo and Freight, Policy [Policy Text Block]	0.0	0.0
Parent [Member]
Profitability
Income tax benefit	$ 17.2	$ 11.9