Financial Data of Busines Segments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Lease Income	$ 1,381.1	$ 1,251.4	$ 1,154.6
MarineOperatingRevenue	0.0	6.9	18.9
Other revenue	139.8	115.0	98.0
Total Revenues	1,585.5	1,410.9	1,273.0
Maintenance Expense	381.6	344.8	292.7
Depreciation expense	402.4	376.3	357.5
Marine operating expense	0.0	6.5	14.1
Operating Lease, Expense	33.9	36.0	36.1
Other operating expense	57.7	46.6	37.4
Total Expenses	875.6	810.2	737.8
Interest Income (Expense), Nonoperating	(341.0)	(263.4)	(214.0)
Other (expense) income	(9.5)	(9.4)	(27.0)
Share of affiliates' earnings (pre-tax)	108.3	98.1	45.9
Segment Profit Loss	606.0	556.3	418.0
Selling, general and administrative	236.3	212.7	195.0
Income tax benefit	60.0	58.7	54.8
Net Income	284.2	259.2	155.9
Disposition Gains on Owned Assets	122.0	119.8	104.1
Nonoperating Income, Residual Sharing Income	0.5	0.9	5.6
Asset Impairment Charges	0.0	(1.5)	(48.9)
Identifiable assets	12,296.5	11,326.0	10,072.0
Nonremarketing Disposition Gain (Loss)	15.8	11.1	17.1
Portfolio Investments and Capital Additions	1,674.4	1,665.0	1,255.8
Investments in Affiliated Companies	663.3	627.0	575.1
Provision for Income Taxes, Equity Method Investment	25.5	25.7	12.3
Non-dedicated engine revenue	64.6	37.6	1.5
Net gain on asset dispositions	138.3	130.3	77.9
Parent [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Income tax benefit	85.5	84.4	67.1
Other Business Segments [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Lease Income	31.6	33.4	29.4
MarineOperatingRevenue		0.0	0.0
Other revenue	7.5	8.1	6.7
Total Revenues	39.1	41.5	36.1
Maintenance Expense	4.0	4.1	2.8
Depreciation expense	14.8	13.9	12.0
Marine operating expense		0.0	0.0
Operating Lease, Expense	0.0	0.0	0.0
Other operating expense	4.3	3.0	2.3
Total Expenses	23.1	21.0	17.1
Interest Income (Expense), Nonoperating	4.4	5.5	(4.8)
Other (expense) income	(7.9)	2.6	(18.6)
Share of affiliates' earnings (pre-tax)	0.0	0.0	0.0
Segment Profit Loss	12.9	29.2	(3.9)
Disposition Gains on Owned Assets	0.3	0.3	0.3
Nonoperating Income, Residual Sharing Income	0.0	0.0	0.0
Asset Impairment Charges		0.0	0.0
Identifiable assets	658.2	801.9	745.3
Nonremarketing Disposition Gain (Loss)	0.1	0.3	0.2
Portfolio Investments and Capital Additions	18.3	38.4	46.3
Investments in Affiliated Companies	0.0	0.0	0.0
Net gain on asset dispositions	0.4	0.6	0.5
Rail North America [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Lease Income	983.5	888.8	826.0
MarineOperatingRevenue		0.0	0.0
Other revenue	115.5	93.9	82.0
Total Revenues	1,099.0	982.7	908.0
Maintenance Expense	306.9	276.6	238.5
Depreciation expense	271.1	265.9	258.6
Marine operating expense		0.0	0.0
Operating Lease, Expense	33.9	36.0	36.1
Other operating expense	26.4	25.9	24.5
Total Expenses	638.3	604.4	557.7
Interest Income (Expense), Nonoperating	(232.1)	(182.9)	(144.6)
Other (expense) income	(5.4)	(8.0)	(4.6)
Share of affiliates' earnings (pre-tax)	0.0	(0.6)	0.5
Segment Profit Loss	356.0	307.3	321.3
Disposition Gains on Owned Assets	119.4	111.7	102.2
Nonoperating Income, Residual Sharing Income	0.5	0.4	2.4
Asset Impairment Charges		0.0	0.0
Identifiable assets	7,751.6	6,993.8	6,445.7
Nonremarketing Disposition Gain (Loss)	12.9	8.4	15.1
Portfolio Investments and Capital Additions	1,162.4	976.9	815.9
Investments in Affiliated Companies			0.8
Net gain on asset dispositions	132.8	120.5	119.7
Rail North America [Member] | RailPulse
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Investments in Affiliated Companies	0.2	0.2
Rail International [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Lease Income	333.6	296.6	266.2
MarineOperatingRevenue		0.0	0.0
Other revenue	16.7	12.9	9.1
Total Revenues	350.3	309.5	275.3
Maintenance Expense	70.7	64.1	51.4
Depreciation expense	78.7	68.2	69.1
Marine operating expense		0.0	0.0
Operating Lease, Expense	0.0	0.0	0.0
Other operating expense	17.4	10.4	8.3
Total Expenses	166.8	142.7	128.8
Interest Income (Expense), Nonoperating	(71.4)	(56.2)	(45.6)
Other (expense) income	3.2	(4.2)	(3.8)
Share of affiliates' earnings (pre-tax)	0.0	0.0	0.0
Segment Profit Loss	119.8	113.4	85.9
Disposition Gains on Owned Assets	1.7	4.9	1.6
Nonoperating Income, Residual Sharing Income	0.0	0.0	0.0
Asset Impairment Charges	0.0	(0.3)	(14.6)
Identifiable assets	2,233.3	2,175.2	1,774.4
Nonremarketing Disposition Gain (Loss)	2.8	2.4	1.8
Portfolio Investments and Capital Additions	232.9	382.4	243.9
Investments in Affiliated Companies	0.0	0.0	0.0
Net gain on asset dispositions	4.5	7.0	(11.2)
Portfolio Management [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Lease Income	32.4	32.6	33.0
MarineOperatingRevenue		6.9	18.9
Other revenue	0.1	0.1	0.2
Total Revenues	97.1	77.2	53.6
Maintenance Expense	0.0	0.0	0.0
Depreciation expense	37.8	28.3	17.8
Marine operating expense		6.5	14.1
Operating Lease, Expense	0.0	0.0	0.0
Other operating expense	9.6	7.3	2.3
Total Expenses	47.4	42.1	34.2
Interest Income (Expense), Nonoperating	(41.9)	(29.8)	(19.0)
Other (expense) income	0.6	0.2	0.0
Share of affiliates' earnings (pre-tax)	108.3	98.7	45.4
Segment Profit Loss	117.3	106.4	14.7
Disposition Gains on Owned Assets	0.6	2.9	0.0
Nonoperating Income, Residual Sharing Income	0.0	0.5	3.2
Asset Impairment Charges	0.0	(1.2)	(34.3)
Identifiable assets	1,653.4	1,355.1	1,106.6
Nonremarketing Disposition Gain (Loss)	0.0	0.0	0.0
Portfolio Investments and Capital Additions	260.8	267.3	149.7
Investments in Affiliated Companies	663.1	626.8	574.3
Non-dedicated engine revenue	64.6	37.6	1.5
Net gain on asset dispositions	0.6	2.2	$ (31.1)
Portfolio Management [Member] | Rolls Royce Partners Finance [Member]
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Investments in Affiliated Companies	$ 663.1	$ 626.8