Note 14. Earnings Per Common Share Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Weighted Average Number of Shares Outstanding, Basic and Diluted	4.5	5.5	5.8
Income (loss) from continuing operations	$ (226.1)	$ 139.2	$ 109.0
Less: Net (income) loss attributable to noncontrolling interest	78.9	1.5	(3.8)
Unvested restricted share participation — continuing operations	0.0	(1.8)	(2.2)
Net income (loss) from continuing operations attributable to Trinity Industries, Inc.	(147.2)	138.9	103.0
Income (loss) from discontinued operations, net of provision (benefit) for income taxes of $(0.1), $(1.0), $30.7	(0.1)	(3.1)	54.1
Unvested restricted share participation — discontinued operations	0.0	0.0	(0.6)
Net income (loss) from discontinued operations attributable to Trinity Industries, Inc.	(0.1)	(3.1)	53.5
Net income (loss) attributable to Trinity Industries, Inc., including the effect of unvested restricted share participation	$ (147.3)	$ 135.8	$ 156.5
Basic weighted average shares outstanding	115.9	125.6	144.0
Nonparticipating unvested RSUs and RSAs	0.0	1.7	1.0
Convertible subordinated notes	0.0	0.0	1.4
Diluted weighted average shares outstanding	115.9	127.3	146.4
Income (loss) from continuing operations	$ (1.27)	$ 1.11	$ 0.72
Income (loss) from discontinued operations	0	(0.02)	0.37
Basic net income (loss) attributable to Trinity Industries, Inc.	(1.27)	1.09	1.09
Income (loss) from continuing operations	(1.27)	1.09	0.70
Income (loss) from discontinued operations	0	(0.02)	0.37
Diluted net income (loss) attributable to Trinity Industries, Inc.	$ (1.27)	$ 1.07	$ 1.07
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	0.0	0.2	0.0
Share-based Payment Arrangement, Option [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	0.0