Financial Data of Business Segments (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($) AircraftEngines	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) AircraftEngines Segment	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Segment Reporting Information [Line Items]
Provision for Income Taxes, Equity Method Investment	$ 24.0	$ 3.0	$ 33.1	$ 10.0
Number of business segments | Segment			3
Profitability
Lease revenue	273.3	270.5	$ 813.3	816.8
Other revenue	26.1	26.4	79.4	80.4
Total Revenues	304.4	298.8	904.3	901.6
Maintenance expense	76.7	76.2	244.8	235.3
Marine operating expense	3.6	3.4	10.9	12.0
Depreciation	83.4	80.0	245.4	240.2
Operating lease expense	12.3	13.7	38.1	41.1
Other operating expense	8.3	7.7	26.0	23.5
Total Expenses	184.3	181.0	565.2	552.1
Net gain on asset dispositions	8.9	5.1	42.3	46.9
Interest expense, net	(48.6)	(44.7)	(141.5)	(135.3)
Other (expense) income	(1.2)	(1.7)	(12.2)	(5.3)
Share of affiliates' earnings (pre-tax)	46.8	15.8	93.2	53.6
Segment profit (loss)	126.0	92.3	320.9	309.4
SG&A	42.0	42.6	125.8	129.6
Income tax benefit	11.8	9.5	29.6	31.1
Net Income	48.2	37.2	132.4	138.7
Net income (loss) from discontinued operations, net of taxes	0.0	7.9	(2.2)	15.9
(Loss) gain on sale of discontinued operations, net of taxes	(0.3)	0.0	3.3	0.0
Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	(0.3)	7.9	1.1	15.9
Net income	47.9	45.1	133.5	154.6
Disposition Gains on Owned Assets	8.0	4.4	39.4	40.9
Nonoperating Income, Residual Sharing Income	0.6	0.6	1.8	1.4
Nonremarketing Disposition Gain (Loss)	0.3	0.1	1.1	4.6
Selected Balance Sheet Data
Investments in affiliated companies	582.5		582.5		$ 512.6
Identifiable assets from continuing operations	8,690.3		8,690.3		7,994.0
Identifiable assets from discontinued operations	0.0		0.0		291.1
Capital Expenditures
Portfolio investments and capital additions	(249.9)	(190.8)	(641.4)	(503.8)
Marine operating revenue	5.0	1.9	11.6	4.4
Rail North America [Member]
Profitability
Lease revenue	208.7	214.6	630.8	654.3
Other revenue	23.4	23.9	72.5	73.7
Total Revenues	232.1	238.5	703.3	728.0
Maintenance expense	63.2	64.0	206.5	199.8
Marine operating expense	0.0	0.0	0.0	0.0
Depreciation	65.0	63.9	193.0	192.6
Operating lease expense	12.3	13.7	38.1	41.1
Other operating expense	6.6	6.2	20.8	19.0
Total Expenses	147.1	147.8	458.4	452.5
Net gain on asset dispositions	7.9	4.3	39.9	44.6
Interest expense, net	(35.7)	(33.1)	(103.5)	(101.4)
Other (expense) income	(1.1)	(1.0)	(3.2)	(3.6)
Share of affiliates' earnings (pre-tax)	0.0	0.0	0.0	0.0
Segment profit (loss)	56.1	60.9	178.1	215.1
Disposition Gains on Owned Assets	7.8	4.4	39.1	40.9
Nonoperating Income, Residual Sharing Income	0.1	0.1	0.3	0.3
Nonremarketing Disposition Gain (Loss)	0.0	(0.2)	0.5	3.4
Selected Balance Sheet Data
Investments in affiliated companies	0.2		0.2		0.2
Identifiable assets from continuing operations	5,838.9		5,838.9		5,646.7
Identifiable assets from discontinued operations					0.0
Capital Expenditures
Portfolio investments and capital additions	(204.1)	(138.1)	(474.6)	(342.4)
Marine operating revenue	0.0	0.0	0.0	0.0
Rail International [Member]
Profitability
Lease revenue	64.5	55.6	181.9	161.7
Other revenue	2.6	2.4	6.5	6.2
Total Revenues	67.1	58.0	188.4	167.9
Maintenance expense	13.5	12.2	38.3	35.5
Marine operating expense	0.0	0.0	0.0	0.0
Depreciation	17.1	14.5	48.4	42.7
Operating lease expense	0.0	0.0	0.0	0.0
Other operating expense	1.6	1.4	4.9	4.2
Total Expenses	32.2	28.1	91.6	82.4
Net gain on asset dispositions	0.5	0.3	0.8	1.2
Interest expense, net	(11.9)	(10.2)	(34.0)	(30.2)
Other (expense) income	0.5	(0.1)	(5.7)	(0.5)
Share of affiliates' earnings (pre-tax)	0.0	0.0	0.0	0.0
Segment profit (loss)	24.0	19.9	57.9	56.0
Disposition Gains on Owned Assets	0.2	0.0	0.2	0.0
Nonoperating Income, Residual Sharing Income	0.0	0.0	0.0	0.0
Nonremarketing Disposition Gain (Loss)	0.3	0.3	0.6	1.2
Selected Balance Sheet Data
Investments in affiliated companies	0.0		0.0		0.0
Identifiable assets from continuing operations	1,654.3		1,654.3		1,486.7
Identifiable assets from discontinued operations					0.0
Capital Expenditures
Portfolio investments and capital additions	(45.3)	(51.8)	(164.5)	(158.6)
Marine operating revenue	0.0	0.0	0.0	0.0
Portfolio Management [Member]
Profitability
Lease revenue	0.1	0.3	0.6	0.8
Other revenue	0.1	0.1	0.4	0.5
Total Revenues	5.2	2.3	12.6	5.7
Maintenance expense	0.0	0.0	0.0	0.0
Marine operating expense	3.6	3.4	10.9	12.0
Depreciation	1.3	1.6	4.0	4.9
Operating lease expense	0.0	0.0	0.0	0.0
Other operating expense	0.1	0.1	0.3	0.3
Total Expenses	5.0	5.1	15.2	17.2
Net gain on asset dispositions	0.5	0.5	1.6	1.1
Interest expense, net	(3.2)	(2.8)	(9.1)	(8.3)
Other (expense) income	0.0	0.0	0.0	0.0
Share of affiliates' earnings (pre-tax)	46.8	15.8	93.2	53.6
Segment profit (loss)	44.3	10.7	83.1	34.9
Disposition Gains on Owned Assets	0.0	0.0	0.1	0.0
Nonoperating Income, Residual Sharing Income	0.5	0.5	1.5	1.1
Nonremarketing Disposition Gain (Loss)	0.0	0.0	0.0	0.0
Selected Balance Sheet Data
Investments in affiliated companies	582.3		582.3		512.4
Identifiable assets from continuing operations	709.7		709.7		653.7
Identifiable assets from discontinued operations					0.0
Capital Expenditures
Portfolio investments and capital additions	0.0	0.0	(0.3)	0.0
Marine operating revenue	$ 5.0	1.9	$ 11.6	4.4
Number of Specialized Gas Vessels | AircraftEngines	5		5
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	1.4	5.1	4.6
Other (expense) income	(0.6)	(0.6)	(3.3)	(1.2)
Share of affiliates' earnings (pre-tax)	0.0	0.0	0.0	0.0
Segment profit (loss)	1.6	0.8	1.8	3.4
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 from continuing operations	487.4		487.4		206.9
Identifiable assets from discontinued operations					$ 0.0
Capital Expenditures
Portfolio investments and capital additions	(0.5)	(0.9)	(2.0)	(2.8)
Marine operating revenue	0.0	0.0	0.0	0.0
Parent [Member]
Profitability
Income tax benefit	$ 35.8	$ 12.5	$ 62.7	$ 41.1