Financial Data of Business Segments (Details) $ in Millions	3 Months Ended				9 Months Ended		12 Months Ended
	Sep. 30, 2023 USD ($) AircraftEngines	Jun. 30, 2023 USD ($) AircraftEngines	Mar. 31, 2023 USD ($) AircraftEngines	Sep. 30, 2022 USD ($) AircraftEngines	Sep. 30, 2023 USD ($) AircraftEngines Segment	Sep. 30, 2022 USD ($)	Dec. 31, 2022 USD ($)	Jun. 30, 2022 AircraftEngines
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Net Income (Loss) Attributable to Parent	$ 52.5			$ 29.1	$ 193.2	$ 107.5
Provision for Income Taxes, Equity Method Investment	4.5			2.5	17.7	6.0
Lease Income	317.2			292.4	927.8	860.6
Marine operating revenue	0.6			4.8	6.1	16.2
Other Operating Income	42.3			23.8	108.3	73.5
Total Revenues	360.1			321.0	1,042.2	950.3
Cost of Property Repairs and Maintenance	87.9			75.9	254.1	221.3
Marine operating expense	1.0			3.6	5.4	11.7
Depreciation	96.2			88.7	278.1	268.2
Operating Lease, Expense	9.0			9.0	27.0	27.1
Other operating expense	12.0			8.7	34.0	28.7
Total Expenses	206.1			185.9	598.6	557.0
Gain (Loss) on Disposition of Assets, Net	16.9			3.9	105.1	53.4
Interest expense, net	(68.1)			(53.6)	(190.8)	(156.7)
Other (expense) income	1.8			(2.5)	(7.1)	(15.8)
Share of affiliates' earnings (pre-tax)	17.9			10.0	65.8	20.8
Segment profit (loss)	122.5			92.9	416.6	295.0
Income tax benefit	14.5			13.7	52.3	38.8
Selling, general and administrative	51.0			47.6	153.4	142.7
Disposition Gains on Owned Assets	13.1			9.1	94.7	75.6
Nonoperating Income, Residual Sharing Income	0.3			1.0	0.7	4.7
Nonremarketing Disposition Gain (Loss)	3.5			4.6	10.9	15.4
Portfolio Investments and Capital Additions	363.9			203.4	1,237.5	887.9
Identifiable assets	10,647.5				10,647.5
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures	(626.9)				(626.9)		$ (575.1)
Assets	(10,647.5)				$ (10,647.5)		(10,072.0)
Number of business segments | Segment					3
Asset Impairment Charges	$ 0.0			10.8	$ 1.2	42.3
Number of Specialized Gas Vessels | AircraftEngines								5
Number of Specialized Gas Vessels Sold | AircraftEngines		1	1
Number of Aircraft Engines Acquired | AircraftEngines	1	9
Number of Aircraft Engines Acquired | AircraftEngines	1	9
Segment Reporting Information [Line Items]
Lease Income	$ 317.2			292.4	927.8	860.6
Marine operating revenue	0.6			4.8	6.1	16.2
Other Operating Income	42.3			23.8	108.3	73.5
Total Revenues	360.1			321.0	1,042.2	950.3
Cost of Property Repairs and Maintenance	87.9			75.9	254.1	221.3
Marine operating expense	1.0			3.6	5.4	11.7
Depreciation	96.2			88.7	278.1	268.2
Operating Lease, Expense	9.0			9.0	27.0	27.1
Other operating expense	12.0			8.7	34.0	28.7
Operating Costs and Expenses	206.1			185.9	598.6	557.0
Gain (Loss) on Disposition of Assets, Net	16.9			3.9	105.1	53.4
Interest Expense	68.1			53.6	190.8	156.7
Other (expense) income	1.8			(2.5)	(7.1)	(15.8)
Share of affiliates' earnings (pre-tax)	17.9			10.0	65.8	20.8
Segment Profit Loss	122.5			92.9	416.6	295.0
Portfolio Investments and Capital Additions	363.9			203.4	1,237.5	887.9
Net Income (Loss) Attributable to Parent	52.5			29.1	193.2	107.5
Disposition Gains on Owned Assets	13.1			9.1	94.7	75.6
Nonoperating Income, Residual Sharing Income	0.3			1.0	0.7	4.7
Nonremarketing Disposition Gain (Loss)	3.5			4.6	10.9	15.4
Asset Impairment Charges	0.0			10.8	1.2	42.3
Parent [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Income tax benefit	19.0			16.2	70.0	44.8
Rail North America
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Lease Income	225.2			211.3	659.2	615.0
Marine operating revenue	0.0			0.0	0.0	0.0
Other Operating Income	22.7			20.0	68.0	61.8
Total Revenues	247.9			231.3	727.2	676.8
Cost of Property Repairs and Maintenance	69.4			62.4	203.1	180.1
Marine operating expense	0.0			0.0	0.0	0.0
Depreciation	66.9			65.3	198.5	193.7
Operating Lease, Expense	9.0			9.0	27.0	27.1
Other operating expense	6.5			6.0	20.2	19.2
Total Expenses	151.8			142.7	448.8	420.1
Gain (Loss) on Disposition of Assets, Net	15.5			13.3	97.4	90.0
Interest expense, net	(46.6)			(36.5)	(133.4)	(105.8)
Other (expense) income	1.2			(1.4)	(1.3)	(3.4)
Share of affiliates' earnings (pre-tax)	(0.1)			0.3	(0.5)	0.3
Segment profit (loss)	66.1			64.3	240.6	237.8
Disposition Gains on Owned Assets	13.0			8.8	88.4	74.4
Nonoperating Income, Residual Sharing Income	0.1			0.2	0.3	2.3
Nonremarketing Disposition Gain (Loss)	2.4			4.3	8.7	13.3
Portfolio Investments and Capital Additions	197.0			142.5	654.8	676.6
Identifiable assets	6,778.4				6,778.4		6,445.7
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures	(0.4)				(0.4)		0.8
Asset Impairment Charges					0.0
Segment Reporting Information [Line Items]
Lease Income	225.2			211.3	659.2	615.0
Marine operating revenue	0.0			0.0	0.0	0.0
Other Operating Income	22.7			20.0	68.0	61.8
Total Revenues	247.9			231.3	727.2	676.8
Cost of Property Repairs and Maintenance	69.4			62.4	203.1	180.1
Marine operating expense	0.0			0.0	0.0	0.0
Depreciation	66.9			65.3	198.5	193.7
Operating Lease, Expense	9.0			9.0	27.0	27.1
Other operating expense	6.5			6.0	20.2	19.2
Operating Costs and Expenses	151.8			142.7	448.8	420.1
Gain (Loss) on Disposition of Assets, Net	15.5			13.3	97.4	90.0
Interest Expense	46.6			36.5	133.4	105.8
Other (expense) income	1.2			(1.4)	(1.3)	(3.4)
Share of affiliates' earnings (pre-tax)	(0.1)			0.3	(0.5)	0.3
Segment Profit Loss	66.1			64.3	240.6	237.8
Portfolio Investments and Capital Additions	197.0			142.5	654.8	676.6
Disposition Gains on Owned Assets	13.0			8.8	88.4	74.4
Nonoperating Income, Residual Sharing Income	0.1			0.2	0.3	2.3
Nonremarketing Disposition Gain (Loss)	2.4			4.3	8.7	13.3
Asset Impairment Charges					0.0
Rail International
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Lease Income	75.6			65.3	219.1	199.4
Marine operating revenue	0.0			0.0	0.0	0.0
Other Operating Income	3.6			2.3	9.6	6.5
Total Revenues	79.2			67.6	228.7	205.9
Cost of Property Repairs and Maintenance	17.1			12.8	47.6	39.0
Marine operating expense	0.0			0.0	0.0	0.0
Depreciation	17.5			16.8	49.8	52.0
Operating Lease, Expense	0.0			0.0	0.0	0.0
Other operating expense	2.7			1.5	7.2	6.0
Total Expenses	37.3			31.1	104.6	97.0
Gain (Loss) on Disposition of Assets, Net	0.9			(10.3)	2.4	(7.9)
Interest expense, net	(14.5)			(11.2)	(40.5)	(33.5)
Other (expense) income	(0.1)			(0.5)	(7.0)	0.2
Share of affiliates' earnings (pre-tax)	0.0			0.0	0.0	0.0
Segment profit (loss)	28.2			14.5	79.0	67.7
Disposition Gains on Owned Assets	0.0			0.3	0.5	1.0
Nonoperating Income, Residual Sharing Income	0.0			0.0	0.0	0.0
Nonremarketing Disposition Gain (Loss)	0.9			0.2	1.9	1.9
Portfolio Investments and Capital Additions	129.6			50.1	288.0	177.8
Identifiable assets	1,979.2				1,979.2		1,774.4
Asset Impairment Charges				10.8	0.0	10.8	14.6
Segment Reporting Information [Line Items]
Lease Income	75.6			65.3	219.1	199.4
Marine operating revenue	0.0			0.0	0.0	0.0
Other Operating Income	3.6			2.3	9.6	6.5
Total Revenues	79.2			67.6	228.7	205.9
Cost of Property Repairs and Maintenance	17.1			12.8	47.6	39.0
Marine operating expense	0.0			0.0	0.0	0.0
Depreciation	17.5			16.8	49.8	52.0
Operating Lease, Expense	0.0			0.0	0.0	0.0
Other operating expense	2.7			1.5	7.2	6.0
Operating Costs and Expenses	37.3			31.1	104.6	97.0
Gain (Loss) on Disposition of Assets, Net	0.9			(10.3)	2.4	(7.9)
Interest Expense	14.5			11.2	40.5	33.5
Other (expense) income	(0.1)			(0.5)	(7.0)	0.2
Share of affiliates' earnings (pre-tax)	0.0			0.0	0.0	0.0
Segment Profit Loss	28.2			14.5	79.0	67.7
Portfolio Investments and Capital Additions	129.6			50.1	288.0	177.8
Disposition Gains on Owned Assets	0.0			0.3	0.5	1.0
Nonoperating Income, Residual Sharing Income	0.0			0.0	0.0	0.0
Nonremarketing Disposition Gain (Loss)	0.9			0.2	1.9	1.9
Asset Impairment Charges				10.8	0.0	10.8	14.6
Portfolio Management
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Lease Income	8.1			8.3	24.5	24.8
Marine operating revenue	0.6			4.8	6.1	16.2
Other Operating Income	13.7			0.0	24.6	0.1
Total Revenues	22.4			13.1	55.2	41.1
Cost of Property Repairs and Maintenance	0.0			0.0	0.0	0.0
Marine operating expense	1.0			3.6	5.4	11.7
Depreciation	8.4			3.7	19.9	13.6
Operating Lease, Expense	0.0			0.0	0.0	0.0
Other operating expense	2.1			0.6	4.4	1.7
Total Expenses	11.5			7.9	29.7	27.0
Gain (Loss) on Disposition of Assets, Net	0.2			0.8	4.7	(29.1)
Interest expense, net	(8.7)			(4.6)	(20.9)	(13.9)
Other (expense) income	(0.2)			0.1	(0.5)	0.0
Share of affiliates' earnings (pre-tax)	18.0			9.7	66.3	20.5
Segment profit (loss)	20.2			11.2	75.1	(8.4)
Disposition Gains on Owned Assets	0.0			0.0	5.5	0.0
Nonoperating Income, Residual Sharing Income	0.2			0.8	0.4	2.4
Nonremarketing Disposition Gain (Loss)	0.0			0.0	0.0	0.0
Portfolio Investments and Capital Additions	28.3	$ 239.0		0.0	267.3	0.0
Identifiable assets	1,369.4				1,369.4		1,106.6
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures	$ (626.5)				(626.5)		574.3
Asset Impairment Charges			$ 1.2	$ 0.0	$ 1.2	31.5	34.3
Number of Specialized Gas Vessels | AircraftEngines	1		2		1
Number of Specialized Gas Vessels Sold | AircraftEngines		1	1	2
Number of Aircraft Engines Acquired | AircraftEngines					10
Number of Aircraft Engines Acquired | AircraftEngines					10
Segment Reporting Information [Line Items]
Lease Income	$ 8.1			$ 8.3	$ 24.5	24.8
Marine operating revenue	0.6			4.8	6.1	16.2
Other Operating Income	13.7			0.0	24.6	0.1
Total Revenues	22.4			13.1	55.2	41.1
Cost of Property Repairs and Maintenance	0.0			0.0	0.0	0.0
Marine operating expense	1.0			3.6	5.4	11.7
Depreciation	8.4			3.7	19.9	13.6
Operating Lease, Expense	0.0			0.0	0.0	0.0
Other operating expense	2.1			0.6	4.4	1.7
Operating Costs and Expenses	11.5			7.9	29.7	27.0
Gain (Loss) on Disposition of Assets, Net	0.2			0.8	4.7	(29.1)
Interest Expense	8.7			4.6	20.9	13.9
Other (expense) income	(0.2)			0.1	(0.5)	0.0
Share of affiliates' earnings (pre-tax)	18.0			9.7	66.3	20.5
Segment Profit Loss	20.2			11.2	75.1	(8.4)
Portfolio Investments and Capital Additions	28.3	$ 239.0		0.0	267.3	0.0
Disposition Gains on Owned Assets	0.0			0.0	5.5	0.0
Nonoperating Income, Residual Sharing Income	0.2			0.8	0.4	2.4
Nonremarketing Disposition Gain (Loss)	0.0			0.0	0.0	0.0
Asset Impairment Charges			$ 1.2	0.0	1.2	31.5	34.3
Other
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Lease Income	8.3			7.5	25.0	21.4
Marine operating revenue	0.0			0.0	0.0	0.0
Other Operating Income	2.3			1.5	6.1	5.1
Total Revenues	10.6			9.0	31.1	26.5
Cost of Property Repairs and Maintenance	1.4			0.7	3.4	2.2
Marine operating expense	0.0			0.0	0.0	0.0
Depreciation	3.4			2.9	9.9	8.9
Operating Lease, Expense	0.0			0.0	0.0	0.0
Other operating expense	0.7			0.6	2.2	1.8
Total Expenses	5.5			4.2	15.5	12.9
Gain (Loss) on Disposition of Assets, Net	0.3			0.1	0.6	0.4
Interest expense, net	1.7			(1.3)	4.0	(3.5)
Other (expense) income	0.9			(0.7)	1.7	(12.6)
Share of affiliates' earnings (pre-tax)	0.0			0.0	0.0	0.0
Segment profit (loss)	8.0			2.9	21.9	(2.1)
Disposition Gains on Owned Assets	0.1			0.0	0.3	0.2
Nonoperating Income, Residual Sharing Income	0.0			0.0	0.0	0.0
Nonremarketing Disposition Gain (Loss)	0.2			0.1	0.3	0.2
Portfolio Investments and Capital Additions	9.0			10.8	27.4	33.5
Identifiable assets	520.5				520.5		$ 745.3
Segment Reporting Information [Line Items]
Lease Income	8.3			7.5	25.0	21.4
Marine operating revenue	0.0			0.0	0.0	0.0
Other Operating Income	2.3			1.5	6.1	5.1
Total Revenues	10.6			9.0	31.1	26.5
Cost of Property Repairs and Maintenance	1.4			0.7	3.4	2.2
Marine operating expense	0.0			0.0	0.0	0.0
Depreciation	3.4			2.9	9.9	8.9
Operating Lease, Expense	0.0			0.0	0.0	0.0
Other operating expense	0.7			0.6	2.2	1.8
Operating Costs and Expenses	5.5			4.2	15.5	12.9
Gain (Loss) on Disposition of Assets, Net	0.3			0.1	0.6	0.4
Interest Expense	(1.7)			1.3	(4.0)	3.5
Other (expense) income	0.9			(0.7)	1.7	(12.6)
Share of affiliates' earnings (pre-tax)	0.0			0.0	0.0	0.0
Segment Profit Loss	8.0			2.9	21.9	(2.1)
Portfolio Investments and Capital Additions	9.0			10.8	27.4	33.5
Disposition Gains on Owned Assets	0.1			0.0	0.3	0.2
Nonoperating Income, Residual Sharing Income	0.0			0.0	0.0	0.0
Nonremarketing Disposition Gain (Loss)	$ 0.2			$ 0.1	$ 0.3	$ 0.2