Earnings Per Common Share - EPS calculation (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Total weighted average restricted shares and antidilutive stock options (in shares)	5.4	6.2
Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	$ 31.2	$ 15.2
Net Income (Loss) Attributable to Noncontrolling Interest	0.5	(1.4)
Unvested restricted share participation	(0.5)	(0.4)
Net Income (Loss) from Continuing Operations Available to Common Shareholders, Basic	31.2	13.4
Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	(1.1)	26.4
Undistributed Discontinued Operation Earnings (Loss), Allocation to Participating Securities, Basic	0.0	(0.3)
Net Income (Loss) from Discontinued Operations Available to Common Shareholders, Basic	(1.1)	26.1
Net Income (Loss) Available to Common Stockholders	$ 30.1	$ 39.5
Income (Loss) from Continuing Operations, Per Basic Share	$ 0.24	$ 0.09
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Basic Share	(0.01)	0.18
Net income attributable to Trinity Industries, Inc. - basic, EPS (in dollars per share)	0.23	0.27
Income (Loss) from Continuing Operations, Per Diluted Share	0.24	0.09
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Diluted Share	(0.01)	0.17
Net income attributable to Trinity Industries, Inc. - diluted, EPS (in dollars per share)	$ 0.23	$ 0.26
Computation of basic and diluted net income attributable to Trinity Industries, Inc
Net income attributable to Trinity Industries, Inc. - basic, Average Shares (in shares)	130.4	147.4
Effect of dilutive securities:
Nonparticipating unvested restricted shares and stock options, average shares	1.8	0.9
Convertible subordinated notes, Average Shares	0.0	5.4
Net income attributable to Trinity Industries, Inc. - diluted, Average Shares	132.2	153.7