Debt - Components of debt (Details) - USD ($) $ in Millions	Mar. 31, 2026	Dec. 31, 2025
Debt Instrument [Line Items]
Debt:	$ 5,382.3	$ 5,442.5
Recourse
Debt Instrument [Line Items]
Debt:	598.6	598.5
Nonrecourse
Debt Instrument [Line Items]
Debt:	4,783.7	4,844.0
Level 2
Debt Instrument [Line Items]
Long-term Debt, Fair Value	615.6	623.9
Level 3
Debt Instrument [Line Items]
Long-term Debt, Fair Value	3,258.6	3,303.6
Corporate Segment [Member]
Debt Instrument [Line Items]
Debt, Net of Unamortized Premium and Unamortized Discount, Gross of Unamortized Debt Issuance Costs	602.8	603.1
Less: unamortized debt issuance costs	4.2	4.6
7.75% Senior Notes Due 2028 | Senior Notes due 2028 | Corporate Segment [Member]
Debt Instrument [Line Items]
Senior Notes	602.8	603.1
Debt Instrument, Unamortized Premium	2.8	3.1
Wholly Owned Subsidiaries [Member] | Nonrecourse
Debt Instrument [Line Items]
Debt:	4,516.7	4,573.4
Wholly Owned Subsidiaries [Member] | Railcar Leasing and Services Group [Member]
Debt Instrument [Line Items]
Debt, Net of Unamortized Premium and Unamortized Discount, Gross of Unamortized Debt Issuance Costs	4,535.9	4,594.3
Less: unamortized debt issuance costs	19.2	20.9
Wholly Owned Subsidiaries [Member] | Railcar Leasing and Services Group [Member] | Nonrecourse
Debt Instrument [Line Items]
Debt:	4,516.7	4,573.4
Wholly Owned Subsidiaries [Member] | Secured Debt [Member] | Railcar Leasing and Services Group [Member]
Debt Instrument [Line Items]
Debt Instrument, Unamortized Discount	0.2	0.3
Debt, Net of Unamortized Premium and Unamortized Discount, Gross of Unamortized Debt Issuance Costs	3,003.2	3,036.3
Wholly Owned Subsidiaries [Member] | TRL-2023 Term Loan | Line of Credit [Member] | Railcar Leasing and Services Group [Member]
Debt Instrument [Line Items]
Long-term Line of Credit	1,025.3	1,031.9
Debt Instrument, Unamortized Discount	0.6	0.6
Wholly Owned Subsidiaries [Member] | Other Equipment Financing | Railcar Leasing and Services Group [Member]
Debt Instrument [Line Items]
Secured Debt, Other	47.0	47.6
Partially-Owned Subsidiaries [Member] | Nonrecourse
Debt Instrument [Line Items]
Debt:	267.0	270.6
Partially-Owned Subsidiaries [Member] | Railcar Leasing and Services Group [Member]
Debt Instrument [Line Items]
Less: unamortized debt issuance costs	0.5	0.7
Partially-Owned Subsidiaries [Member] | Railcar Leasing and Services Group [Member] | Nonrecourse
Debt Instrument [Line Items]
Debt:	267.0	270.6
Partially-Owned Subsidiaries [Member] | Secured Debt [Member] | Railcar Leasing and Services Group [Member]
Debt Instrument [Line Items]
Debt Instrument, Unamortized Discount	0.0	0.0
Debt, Net of Unamortized Premium and Unamortized Discount, Gross of Unamortized Debt Issuance Costs	267.5	271.3
Revolving Credit Facility [Member] | Line of Credit [Member] | Corporate Segment [Member]
Debt Instrument [Line Items]
Long-term Line of Credit	0.0	0.0
Revolving Credit Facility [Member] | TILC [Member] | TILC Warehouse Facility [Member] | Line of Credit [Member] | Railcar Leasing and Services Group [Member]
Debt Instrument [Line Items]
Long-term Line of Credit	$ 460.4	$ 478.5