Earnings Per Common Share - EPS calculation (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Income (loss) from continuing operations	$ 4.8	$ (287.8)	$ 6.5	$ (125.3)
Less: Net loss attributable to noncontrolling interest	7.9	80.9	9.9	80.3
Unvested restricted share participation – continuing operations	0.0	0.0	0.0	0.0
Net income (loss) from continuing operations attributable to Trinity Industries, Inc.	12.7	(206.9)	16.4	(45.0)
Loss from discontinued operations, net of provision (benefit) for income taxes of $—, $—, $0.4, and $(0.1)	0.0	0.0	(0.4)	(0.2)
Unvested restricted share participation – discontinued operations	0.0	0.0	0.0	0.0
Net loss from discontinued operations attributable to Trinity Industries, Inc.	0.0	0.0	(0.4)	(0.2)
Net income (loss) attributable to Trinity Industries, Inc., including the effect of unvested restricted share participation	$ 12.7	$ (206.9)	$ 16.0	$ (45.2)
Basic weighted average shares outstanding	102.8	117.3	106.4	117.6
Effect of dilutive securities	2.3	0.0	2.5	0.0
Diluted weighted average shares outstanding	105.1	117.3	108.9	117.6
Income (Loss) from Continuing Operations, Per Basic Share	$ 0.12	$ (1.76)	$ 0.15	$ (0.38)
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Basic Share	0	0	0	0
Basic net income (loss) attributable to Trinity Industries, Inc.	0.12	(1.76)	0.15	(0.38)
Income (Loss) from Continuing Operations, Per Diluted Share	0.12	(1.76)	0.15	(0.38)
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Diluted Share	0	0	0	0
Diluted net income (loss) attributable to Trinity Industries, Inc.	$ 0.12	$ (1.76)	$ 0.15	$ (0.38)
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	0.0	0.1	0.0
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