Financial Data of Business Segments (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020 USD ($) AircraftEngines	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) Segment AircraftEngines	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Segment Reporting Information [Line Items]
Provision for Income Taxes, Equity Method Investment		$ 3.5		$ 7.0
Number of business segments | Segment			3
Profitability
Lease revenue	$ 269.3	272.9	$ 540.0	546.3
Other revenue	27.9	24.5	53.3	54.0
Total Revenues	300.5	297.5	599.9	602.8
Maintenance expense	82.3	78.2	168.1	159.1
Marine operating expense	3.2	4.0	7.3	8.6
Depreciation	81.6	80.3	162.0	160.2
Operating lease expense	12.5	13.7	25.8	27.4
Other operating expense	9.2	7.8	17.7	15.8
Total Expenses	188.8	184.0	380.9	371.1
Net gain on asset dispositions	6.0	32.9	33.4	41.8
Interest expense, net	(47.4)	(45.5)	(92.9)	(90.6)
Other (expense) income	(3.0)	(0.4)	(11.0)	(3.6)
Share of affiliates' earnings (pre-tax)	22.6	19.6	46.4	37.8
Segment profit (loss)	89.9	120.1	194.9	217.1
SG&A	43.4	43.0	83.8	87.0
Income tax benefit	4.7	13.3	17.8	21.6
Net Income	37.0	60.3	84.2	101.5
Net (loss) income from discontinued operations, net of taxes	(1.3)	7.7	(2.2)	8.0
Gain on sale of discontinued operations, net of taxes	3.6	0.0	3.6	0.0
Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	2.3	7.7	1.4	8.0
Net income	39.3	68.0	85.6	109.5
Disposition Gains on Owned Assets	4.5	26.8	31.4	36.5
Nonoperating Income, Residual Sharing Income	0.6	0.4	1.2	0.8
Nonremarketing Disposition Gain (Loss)	0.9	5.7	0.8	4.5
Selected Balance Sheet Data
Investments in affiliated companies	551.4		551.4		$ 512.6
Identifiable assets from continuing operations	8,512.7		8,512.7		7,994.0
Identifiable assets from discontinued operations	0.0		0.0		291.1
Capital Expenditures
Portfolio investments and capital additions	(210.5)	(180.2)	(391.5)	(313.0)
Marine operating revenue	3.3	0.1	6.6	2.5
Rail North America [Member]
Profitability
Lease revenue	210.0	218.8	422.1	439.7
Other revenue	25.5	22.4	49.1	49.8
Total Revenues	235.5	241.2	471.2	489.5
Maintenance expense	70.4	67.0	143.3	135.8
Marine operating expense	0.0	0.0	0.0	0.0
Depreciation	64.4	64.4	128.0	128.7
Operating lease expense	12.5	13.7	25.8	27.4
Other operating expense	7.6	6.4	14.2	12.8
Total Expenses	154.9	151.5	311.3	304.7
Net gain on asset dispositions	5.2	32.1	32.0	40.3
Interest expense, net	(34.5)	(34.1)	(67.8)	(68.3)
Other (expense) income	(1.3)	(1.9)	(2.1)	(2.6)
Share of affiliates' earnings (pre-tax)	0.0	0.0	0.0	0.0
Segment profit (loss)	50.0	85.8	122.0	154.2
Disposition Gains on Owned Assets	4.4	26.8	31.3	36.5
Nonoperating Income, Residual Sharing Income	0.1	0.1	0.2	0.2
Nonremarketing Disposition Gain (Loss)	0.7	5.2	0.5	3.6
Selected Balance Sheet Data
Investments in affiliated companies	0.2		0.2		0.2
Identifiable assets from continuing operations	5,758.1		5,758.1		5,646.7
Identifiable assets from discontinued operations					0.0
Capital Expenditures
Portfolio investments and capital additions	(159.6)	(105.3)	(270.5)	(204.3)
Marine operating revenue	0.0	0.0	0.0	0.0
Rail International [Member]
Profitability
Lease revenue	59.1	53.9	117.4	106.1
Other revenue	2.1	1.8	3.9	3.8
Total Revenues	61.2	55.7	121.3	109.9
Maintenance expense	11.9	11.2	24.8	23.3
Marine operating expense	0.0	0.0	0.0	0.0
Depreciation	15.8	14.2	31.3	28.2
Operating lease expense	0.0	0.0	0.0	0.0
Other operating expense	1.5	1.3	3.3	2.8
Total Expenses	29.2	26.7	59.4	54.3
Net gain on asset dispositions	0.2	0.5	0.3	0.9
Interest expense, net	(11.5)	(10.1)	(22.1)	(20.0)
Other (expense) income	(0.7)	1.9	(6.2)	(0.4)
Share of affiliates' earnings (pre-tax)	0.0	0.0	0.0	0.0
Segment profit (loss)	20.0	21.3	33.9	36.1
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)	0.2	0.5	0.3	0.9
Selected Balance Sheet Data
Investments in affiliated companies	0.0		0.0		0.0
Identifiable assets from continuing operations	1,573.5		1,573.5		1,486.7
Identifiable assets from discontinued operations					0.0
Capital Expenditures
Portfolio investments and capital additions	(49.9)	(73.7)	(119.2)	(106.8)
Marine operating revenue	0.0	0.0	0.0	0.0
Portfolio Management [Member]
Profitability
Lease revenue	0.2	0.2	0.5	0.5
Other revenue	0.3	0.3	0.3	0.4
Total Revenues	3.8	0.6	7.4	3.4
Maintenance expense	0.0	0.0	0.0	0.0
Marine operating expense	3.2	4.0	7.3	8.6
Depreciation	1.4	1.7	2.7	3.3
Operating lease expense	0.0	0.0	0.0	0.0
Other operating expense	0.1	0.1	0.2	0.2
Total Expenses	4.7	5.8	10.2	12.1
Net gain on asset dispositions	0.6	0.3	1.1	0.6
Interest expense, net	(3.0)	(2.8)	(5.9)	(5.5)
Other (expense) income	0.0	0.0	0.0	0.0
Share of affiliates' earnings (pre-tax)	22.6	19.6	46.4	37.8
Segment profit (loss)	19.3	11.9	38.8	24.2
Disposition Gains on Owned Assets	0.1	0.0	0.1	0.0
Nonoperating Income, Residual Sharing Income	0.5	0.3	1.0	0.6
Nonremarketing Disposition Gain (Loss)	0.0	0.0	0.0	0.0
Selected Balance Sheet Data
Investments in affiliated companies	551.2		551.2		512.4
Identifiable assets from continuing operations	676.3		676.3		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	$ 3.3	0.1	$ 6.6	2.5
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	1.6	1.5	2.9	3.2
Other (expense) income	(1.0)	(0.4)	(2.7)	(0.6)
Share of affiliates' earnings (pre-tax)	0.0	0.0	0.0	0.0
Segment profit (loss)	0.6	1.1	0.2	2.6
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)	0.0	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	504.8		504.8		206.9
Identifiable assets from discontinued operations					$ 0.0
Capital Expenditures
Portfolio investments and capital additions	(1.0)	(1.2)	(1.5)	(1.9)
Marine operating revenue	0.0	0.0	0.0	0.0
Parent [Member]
Profitability
Income tax benefit	$ 9.5	$ 16.8	$ 26.9	$ 28.6