Financial Data of Business Segments (Details)	3 Months Ended			9 Months Ended
	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)	Mar. 31, 2023 USD ($)	Sep. 30, 2024 USD ($) Segment	Sep. 30, 2023 USD ($)	Dec. 31, 2023 USD ($)
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Net Income (Loss) Attributable to Parent	$ 89,000,000.0	$ 52,500,000		$ 207,700,000	$ 193,200,000
Provision for Income Taxes, Equity Method Investment	8,900,000	4,500,000		17,200,000	17,700,000
Lease Income	351,700,000	317,200,000		1,024,600,000	927,800,000
Marine operating revenue	0	600,000		0	6,100,000
Other Operating Income	35,600,000	28,700,000		102,400,000	83,800,000
Total Revenues	405,400,000	360,100,000		1,172,000,000	1,042,200,000
Cost of Property Repairs and Maintenance	95,900,000	87,900,000		283,900,000	254,100,000
Marine operating expense	0	1,000,000.0		0	5,400,000
Depreciation	103,400,000	96,200,000		297,900,000	278,100,000
Operating Lease, Expense	8,000,000.0	9,000,000.0		26,000,000.0	27,000,000.0
Other operating expense	14,100,000	12,000,000.0		41,500,000	34,000,000.0
Total Expenses	221,400,000	206,100,000		649,300,000	598,600,000
Other (expense) income	(900,000)	1,800,000		(10,900,000)	(7,100,000)
Share of affiliates' earnings (pre-tax)	35,300,000	17,900,000		75,900,000	65,800,000
Segment profit (loss)	178,000,000.0	122,500,000		448,500,000	416,600,000
Income tax benefit	22,900,000	14,500,000		51,900,000	52,300,000
Selling, general and administrative	57,200,000	51,000,000.0		171,700,000	153,400,000
Disposition Gains on Owned Assets	44,900,000	13,100,000		98,400,000	94,700,000
Nonoperating Income, Residual Sharing Income	100,000	300,000		300,000	700,000
Nonremarketing Disposition Gain (Loss)	3,500,000	3,500,000		11,600,000	10,900,000
Portfolio Investments and Capital Additions	504,500,000	363,900,000		1,325,100,000	1,237,500,000
Identifiable assets	12,379,900,000			12,379,900,000
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures	(690,300,000)			(690,300,000)		$ (627,000,000.0)
Assets	(12,379,900,000)			$ (12,379,900,000)		(11,326,000,000)
Number of business segments | Segment				3
Asset Impairment Charges				$ 0	1,200,000
Non-dedicated engine revenue	18,100,000	13,600,000		45,000,000.0	24,500,000
Net gain on asset dispositions	48,500,000	16,900,000		110,300,000	105,100,000
Interest Expense, Nonoperating	88,900,000	68,100,000		249,500,000	190,800,000
Rolls Royce
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Payment for Management Fee	1,100,000	900,000		2,900,000	1,900,000
Payment for Management Fee	1,100,000	900,000		2,900,000	1,900,000
Parent [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Income tax benefit	31,800,000	19,000,000.0		69,100,000	70,000,000.0
Rail North America [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Lease Income	249,200,000	225,200,000		727,800,000	659,200,000
Marine operating revenue		0			0
Other Operating Income	29,300,000	22,700,000		86,100,000	68,000,000.0
Total Revenues	278,500,000	247,900,000		813,900,000	727,200,000
Cost of Property Repairs and Maintenance	77,700,000	69,400,000		228,000,000.0	203,100,000
Marine operating expense		0			0
Depreciation	69,200,000	66,900,000		201,100,000	198,500,000
Operating Lease, Expense	8,000,000.0	9,000,000.0		26,000,000.0	27,000,000.0
Other operating expense	7,000,000.0	6,500,000		20,100,000	20,200,000
Total Expenses	161,900,000	151,800,000		475,200,000	448,800,000
Other (expense) income	(800,000)	1,200,000		(3,200,000)	(1,300,000)
Share of affiliates' earnings (pre-tax)	100,000	(100,000)		100,000	(500,000)
Segment profit (loss)	102,400,000	66,100,000		271,500,000	240,600,000
Disposition Gains on Owned Assets	43,600,000	13,000,000.0		96,300,000	88,400,000
Nonoperating Income, Residual Sharing Income	100,000	100,000		300,000	300,000
Nonremarketing Disposition Gain (Loss)	3,000,000.0	2,400,000		9,200,000	8,700,000
Portfolio Investments and Capital Additions	325,900,000	197,000,000.0		955,700,000	654,800,000
Identifiable assets	7,654,800,000			7,654,800,000		6,993,800,000
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures	(300,000)			(300,000)		200,000
Asset Impairment Charges					0
Net gain on asset dispositions	46,700,000	15,500,000		105,800,000	97,400,000
Interest Expense, Nonoperating	60,200,000	46,600,000		169,900,000	133,400,000
Rail International
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Lease Income	86,300,000	75,600,000		248,900,000	219,100,000
Marine operating revenue		0			0
Other Operating Income	4,300,000	3,600,000		10,600,000	9,600,000
Total Revenues	90,600,000	79,200,000		259,500,000	228,700,000
Cost of Property Repairs and Maintenance	17,000,000.0	17,100,000		52,700,000	47,600,000
Marine operating expense		0			0
Depreciation	20,300,000	17,500,000		58,600,000	49,800,000
Operating Lease, Expense	0	0		0	0
Other operating expense	3,700,000	2,700,000		10,800,000	7,200,000
Total Expenses	41,000,000.0	37,300,000		122,100,000	104,600,000
Other (expense) income	1,100,000	(100,000)		800,000	(7,000,000.0)
Share of affiliates' earnings (pre-tax)	0	0		0	0
Segment profit (loss)	33,900,000	28,200,000		89,200,000	79,000,000.0
Disposition Gains on Owned Assets	1,200,000	0		1,300,000	500,000
Nonoperating Income, Residual Sharing Income	0	0		0	0
Nonremarketing Disposition Gain (Loss)	500,000	900,000		2,400,000	1,900,000
Portfolio Investments and Capital Additions	80,600,000	129,600,000		190,100,000	288,000,000.0
Identifiable assets	2,358,500,000			2,358,500,000		2,175,200,000
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures	0			0		0
Asset Impairment Charges					0
Gain (Loss) on Disposition of Business			$ 300,000
Net gain on asset dispositions	1,700,000	900,000		3,700,000	2,400,000
Interest Expense, Nonoperating	18,500,000	14,500,000		52,700,000	40,500,000
Gain (Loss) on Disposition of Business			$ 300,000
Other
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Lease Income	8,100,000	8,300,000		23,600,000	25,000,000.0
Marine operating revenue		0			0
Other Operating Income	2,000,000.0	2,300,000		5,700,000	6,100,000
Total Revenues	10,100,000	10,600,000		29,300,000	31,100,000
Cost of Property Repairs and Maintenance	1,200,000	1,400,000		3,200,000	3,400,000
Marine operating expense		0		0	0
Depreciation	3,800,000	3,400,000		11,100,000	9,900,000
Operating Lease, Expense	0	0			0
Other operating expense	800,000	700,000		3,600,000	2,200,000
Total Expenses	5,800,000	5,500,000		17,900,000	15,500,000
Other (expense) income	(1,300,000)	900,000		(8,800,000)	1,700,000
Share of affiliates' earnings (pre-tax)	0	0		0	0
Segment profit (loss)	4,200,000	8,000,000.0		6,200,000	21,900,000
Disposition Gains on Owned Assets	100,000	100,000		200,000	300,000
Nonoperating Income, Residual Sharing Income	0	0		0	0
Nonremarketing Disposition Gain (Loss)	0	200,000		0	300,000
Portfolio Investments and Capital Additions	3,200,000	9,000,000.0		13,200,000	27,400,000
Identifiable assets	789,900,000			789,900,000		801,900,000
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures	0			0		0
Asset Impairment Charges					0
Net gain on asset dispositions	100,000	300,000		200,000	600,000
Interest Expense, Nonoperating	(1,100,000)	(1,700,000)		(3,400,000)	(4,000,000.0)
Engine Leasing
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Lease Income	8,100,000	8,100,000		24,300,000	24,500,000
Marine operating revenue		600,000			6,100,000
Other Operating Income	0	100,000		0	100,000
Total Revenues	26,200,000	22,400,000		69,300,000	55,200,000
Cost of Property Repairs and Maintenance	0	0		0	0
Marine operating expense		1,000,000.0			5,400,000
Depreciation	10,100,000	8,400,000		27,100,000	19,900,000
Operating Lease, Expense	0	0		0	0
Other operating expense	2,600,000	2,100,000		7,000,000.0	4,400,000
Total Expenses	12,700,000	11,500,000		34,100,000	29,700,000
Other (expense) income	100,000	(200,000)		300,000	(500,000)
Share of affiliates' earnings (pre-tax)	35,200,000	18,000,000.0		75,800,000	66,300,000
Segment profit (loss)	37,500,000	20,200,000		81,600,000	75,100,000
Disposition Gains on Owned Assets	0	0		600,000	5,500,000
Nonoperating Income, Residual Sharing Income	0	200,000		0	400,000
Nonremarketing Disposition Gain (Loss)	0	0		0	0
Portfolio Investments and Capital Additions	94,800,000	28,300,000		166,100,000	267,300,000
Identifiable assets	1,576,700,000			1,576,700,000		1,355,100,000
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures	(690,000,000.0)			(690,000,000.0)		$ 626,800,000
Asset Impairment Charges					1,200,000
Non-dedicated engine revenue	18,100,000	13,600,000		45,000,000.0	24,500,000
Net gain on asset dispositions	0	200,000		600,000	4,700,000
Interest Expense, Nonoperating	$ 11,300,000	$ 8,700,000		$ 30,300,000	$ 20,900,000