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Note 8. Debt (Details) $ in Millions	12 Months Ended
Note 8. Debt (Details) $ in Millions	Dec. 31, 2020 USD ($) Railcar	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Debt Instrument [Line Items]
Loss on early extinguishment of debt	$ 5.0	$ 0.0	$ 0.0
Debt assumed in railcar purchase from unrelated seller	0.0	0.0	283.9
Corporate Segment [Member]
Debt Instrument [Line Items]
Long-term Debt, Net of Unamortized Discount, Gross of Unamortized Debt Issuance Costs	449.8	524.8
Corporate Segment [Member] \| Senior Notes [Member]
Debt Instrument [Line Items]
Long-term Debt, Net of Unamortized Discount, Gross of Unamortized Debt Issuance Costs	$ 399.8	399.8
Corporate Segment [Member] \| Senior Notes [Member] \| 4.55% Senior Notes Due October 2024 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	4.55%
Debt Instrument, Face Amount	$ 400.0
Revolving Credit Facility [Member] \| Corporate Segment [Member] \| Line of Credit [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Current Borrowing Capacity	450.0
Proceeds from Lines of Credit	545.0
Repayments of Lines of Credit	620.0
Long-term Debt, Net of Unamortized Discount, Gross of Unamortized Debt Issuance Costs	50.0	125.0
Line of Credit Facility, Maximum Borrowing Capacity	$ 364.8
Debt Instrument, Interest Rate, Effective Percentage	1.75%
Line of Credit Facility, Interest Rate at Period End	0.25%
Revolving Credit Facility [Member] \| Corporate Segment [Member] \| Line of Credit [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage	0.30%
Line of Credit Facility, Interest Rate at Period End	0.175%
Revolving Credit Facility [Member] \| Corporate Segment [Member] \| Line of Credit [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Interest Rate at Period End	0.40%
Letter of Credit [Member] \| Corporate Segment [Member] \| Line of Credit [Member]
Debt Instrument [Line Items]
Letters of Credit Outstanding, Amount	$ 35.2
Partially-Owned Subsidiaries [Member] \| Railcar Leasing and Management Services Group [Member]
Debt Instrument [Line Items]
Noncontrolling Interest, Ownership Percentage by Parent	38.00%
Wholly Owned Subsidiaries [Member] \| Secured Debt [Member] \| 2006 Secured Railcar Equipment Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	5.90%
Debt Instrument, Face Amount	$ 355.0
Wholly Owned Subsidiaries [Member] \| Secured Debt [Member] \| 2009 Secured Railcar Equipment Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	6.66%
Debt Instrument, Face Amount	$ 238.3
Wholly Owned Subsidiaries [Member] \| Secured Debt [Member] \| 2010 Secured Railcar Equipment Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	5.19%
Debt Instrument, Face Amount	$ 369.2
Wholly Owned Subsidiaries [Member] \| Secured Debt [Member] \| TILC Warehouse Facility [Member]
Debt Instrument [Line Items]
Repayments of Lines of Credit	22.1
Wholly Owned Subsidiaries [Member] \| Secured Debt [Member] \| TRIHC 2018 Secured Railcar Equipment Notes [Member]
Debt Instrument [Line Items]
Business Combination, Consideration Transferred, Equity Interests Issued and Issuable	$ 75.4
Railcars Acquired \| Railcar	4,150
Debt assumed in railcar purchase from unrelated seller	$ 283.9
Wholly Owned Subsidiaries [Member] \| Secured Debt [Member] \| 2017 Secured Railcar Equipment Notes [Member] [Domain]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage	1.69%
Debt Instrument, Face Amount	$ 225.0		$ 663.0	$ 302.4
Wholly Owned Subsidiaries [Member] \| Secured Debt [Member] \| 2018 Secured Railcar Equipment Notes [Domain]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 482.5
Wholly Owned Subsidiaries [Member] \| Secured Debt [Member] \| 2018 Class A-1 Secured Railcar Equipment Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	3.82%
Debt Instrument, Face Amount	$ 200.0
Wholly Owned Subsidiaries [Member] \| Secured Debt [Member] \| 2018 Class A-2 Secured Railcar Equipment Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	4.62%
Debt Instrument, Face Amount	$ 282.5
Non-Recourse Debt, Gross	$ 282.5
Wholly Owned Subsidiaries [Member] \| Secured Debt [Member] \| 2018 Class A 2020-1 Secured Railcar Equipment Notes [Domain]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	1.96%
Debt Instrument, Face Amount	$ 155.5
Non-Recourse Debt, Gross	152.4
Wholly Owned Subsidiaries [Member] \| Secured Debt [Member] \| Trinity Rail Leasing 2019 [Domain]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 386.5
Wholly Owned Subsidiaries [Member] \| Secured Debt [Member] \| 2019 Secured Railcar Equipment Notes [Domain] [Domain]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	3.82%
Debt Instrument, Face Amount	$ 528.3
Non-Recourse Debt, Gross	$ 491.1
Wholly Owned Subsidiaries [Member] \| Secured Debt [Member] \| 2019 Secured Railcar Equipment Notes Class A1 Notes [Domain]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	2.39%
Debt Instrument, Face Amount	$ 106.9
Non-Recourse Debt, Gross	$ 90.1
Wholly Owned Subsidiaries [Member] \| Secured Debt [Member] \| 2019 Secured Railcar Equipment Notes Class A2 Notes [Domain]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	3.10%
Debt Instrument, Face Amount	$ 279.6
Non-Recourse Debt, Gross	$ 279.6
Wholly Owned Subsidiaries [Member] \| Secured Debt [Member] \| 2020 Secured Railcar Equipment Notes Class A1 Notes [Domain]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	1.83%
Debt Instrument, Face Amount	$ 110.0
Non-Recourse Debt, Gross	$ 108.3
Wholly Owned Subsidiaries [Member] \| Secured Debt [Member] \| 2020 Secured Railcar Equipment Notes Class A2 Notes [Domain]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	2.56%
Debt Instrument, Face Amount	$ 240.3
Non-Recourse Debt, Gross	$ 240.3
Wholly Owned Subsidiaries [Member] \| Secured Debt [Member] \| 2020 Secured Railcar Equipment Notes Class B Notes [Domain]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	3.69%
Debt Instrument, Face Amount	$ 20.5
Non-Recourse Debt, Gross	20.5
Wholly Owned Subsidiaries [Member] \| Railcar Leasing and Management Services Group [Member]
Debt Instrument [Line Items]
Non-Recourse Debt, Gross of Issuance Cost, Net of Discount	3,364.5	3,104.6
Wholly Owned Subsidiaries [Member] \| Railcar Leasing and Management Services Group [Member] \| 2006 Secured Railcar Equipment Notes [Member]
Debt Instrument [Line Items]
Extinguishment of Debt, Amount	104.7
Non-Recourse Debt, Gross	0.0	109.3
Loss on early extinguishment of debt	5.0
Redemption Premium	4.7
Amortization of Debt Issuance Costs	0.3
Wholly Owned Subsidiaries [Member] \| Railcar Leasing and Management Services Group [Member] \| 2009 Secured Railcar Equipment Notes [Member]
Debt Instrument [Line Items]
Non-Recourse Debt, Gross	142.3	147.8
Wholly Owned Subsidiaries [Member] \| Railcar Leasing and Management Services Group [Member] \| 2010 Secured Railcar Equipment Notes [Member]
Debt Instrument [Line Items]
Non-Recourse Debt, Gross	235.9	248.5
Wholly Owned Subsidiaries [Member] \| Railcar Leasing and Management Services Group [Member] \| TRIHC 2018 Secured Railcar Equipment Notes [Member]
Debt Instrument [Line Items]
Extinguishment of Debt, Amount	258.6
Non-Recourse Debt, Gross of Issuance Cost, Net of Discount	0.0	265.4
Wholly Owned Subsidiaries [Member] \| Railcar Leasing and Management Services Group [Member] \| 2018 Secured Railcar Equipment Notes [Domain]
Debt Instrument [Line Items]
Non-Recourse Debt, Gross of Issuance Cost, Net of Discount	434.7	452.1
Wholly Owned Subsidiaries [Member] \| Railcar Leasing and Management Services Group [Member] \| 2018 Class A-1 Secured Railcar Equipment Notes [Member]
Debt Instrument [Line Items]
Extinguishment of Debt, Amount	153.1
Wholly Owned Subsidiaries [Member] \| Railcar Leasing and Management Services Group [Member] \| 2019 Secured Railcar Equipment Notes [Domain] [Domain]
Debt Instrument [Line Items]
Non-Recourse Debt, Gross of Issuance Cost, Net of Discount	$ 860.5	901.0
Wholly Owned Subsidiaries [Member] \| Railcar Leasing and Management Services Group [Member] \| Promissory Notes [Member] \| 2017 Secured Railcar Equipment Notes [Member] [Domain]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage	1.50%
Non-Recourse Debt, Gross of Issuance Cost, Net of Discount	$ 802.7	627.1
Repayments of Long-term Lines of Credit	$ 48.3
TILC [Member] \| Revolving Credit Facility [Member] \| Railcar Leasing and Management Services Group [Member] \| Line of Credit [Member] \| TILC Warehouse Facility [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Effective Percentage	1.76%
Debt Instrument, Face Amount	$ 750.0
Long-term Line of Credit	519.4	353.4
Borrowings on Warehouse Loan Facility	283.6
Repayments on Warehouse Loan Facility	117.6
Line of Credit Facility, Remaining Borrowing Capacity	$ 230.6
Partially-Owned Subsidiaries [Member] \| Secured Debt [Member] \| TRIP Master Funding Class A-1a Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	4.37%
Partially-Owned Subsidiaries [Member] \| Secured Debt [Member] \| TRIP Master Funding Class A-1b Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	2.50%
Partially-Owned Subsidiaries [Member] \| Secured Debt [Member] \| TRIP Master Funding Class A-2 Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	6.02%
Non-Recourse Debt, Gross	$ 508.8
Partially-Owned Subsidiaries [Member] \| Secured Debt [Member] \| TRIP Master Funding Series 2014 Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 335.7
Partially-Owned Subsidiaries [Member] \| Secured Debt [Member] \| TRIP Master Funding Series 2014 Class A-1 Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	2.86%
Partially-Owned Subsidiaries [Member] \| Secured Debt [Member] \| TRIP Master Funding Series 2014 Class A-2 Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	4.09%
Non-Recourse Debt, Gross	$ 220.7
Partially-Owned Subsidiaries [Member] \| Secured Debt [Member] \| TRIP Master Funding Series 2017-1 Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 237.9
Partially-Owned Subsidiaries [Member] \| Secured Debt [Member] \| TRIP Master Funding Series 2017-1 Class A-1 Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	2.71%
Non-Recourse Debt, Gross	$ 20.6
Partially-Owned Subsidiaries [Member] \| Secured Debt [Member] \| TRIP Master Funding Series 2017-1 Class A-2 Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	3.74%
Non-Recourse Debt, Gross	$ 134.9
Partially-Owned Subsidiaries [Member] \| Secured Debt [Member] \| TRL 2012 Secured Railcar Equipment Notes - RIV 2013 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	2.27%
Debt Instrument, Face Amount	$ 145.4
Non-Recourse Debt, Gross	$ 25.9
Partially-Owned Subsidiaries [Member] \| Secured Debt [Member] \| TRL 2012 Series 2012-1 Class A-2 Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	3.53%
Debt Instrument, Face Amount	$ 188.4
Non-Recourse Debt, Gross	$ 188.4
Partially-Owned Subsidiaries [Member] \| Secured Debt [Member] \| TRL 2012 Series 2013-1 Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	3.90%
Debt Instrument, Face Amount	$ 183.4
Non-Recourse Debt, Gross	138.2
Partially-Owned Subsidiaries [Member] \| Railcar Leasing and Management Services Group [Member]
Debt Instrument [Line Items]
Non-Recourse Debt, Gross	$ 1,237.5	$ 1,289.3