Earnings Per Common Share - EPS calculation (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Income from continuing operations	$ 23.5	$ 16.5	$ 40.3	$ 26.4
Less: Net income attributable to noncontrolling interest	(4.2)	(4.8)	(13.5)	(7.4)
Net income from continuing operations attributable to Trinity Industries, Inc.	19.3	11.7	26.8	19.0
Loss from discontinued operations, net of benefit for income taxes of $0.7, $0.5, $1.5 and $2.5	(2.3)	(3.4)	(5.4)	(10.3)
Loss on sale of discontinued operations, net of benefit for income taxes of $—, $1.0, $— and $1.4	0.0	(4.6)	0.0	(5.7)
Net loss from discontinued operations attributable to Trinity Industries, Inc.	(2.3)	(8.0)	(5.4)	(16.0)
Net income attributable to Trinity Industries, Inc.	$ 17.0	$ 3.7	$ 21.4	$ 3.0
Basic weighted average shares outstanding	81.2	82.4	81.0	82.7
Effect of dilutive securities	2.2	2.0	2.5	2.2
Diluted weighted average shares outstanding	83.4	84.4	83.5	84.9
Income (Loss) from Continuing Operations, Per Basic Share	$ 0.24	$ 0.14	$ 0.33	$ 0.23
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Basic Share	(0.03)	(0.10)	(0.07)	(0.19)
Basic net income attributable to Trinity Industries, Inc.	0.21	0.04	0.26	0.04
Income (Loss) from Continuing Operations, Per Diluted Share	0.23	0.14	0.32	0.23
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Diluted Share	(0.03)	(0.10)	(0.06)	(0.19)
Diluted net income attributable to Trinity Industries, Inc.	$ 0.20	$ 0.04	$ 0.26	$ 0.04
Restricted Stock [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	0.1	0.1	0.1	0.1
Stock options
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	0.0	0.0	0.0	0.0