Earnings Per Common Share - EPS calculation (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net Income (Loss) Attributable to Noncontrolling Interest	$ 0.6	$ 1.0	$ 3.4	$ 9.6
Total weighted average restricted shares and antidilutive stock options (in shares)	5.9	6.3	5.9	6.4
Computation of basic and diluted net income attributable to Trinity Industries, Inc
Net income attributable to Trinity Industries, Inc.	$ 27.7	$ 66.9	$ 132.0	$ 164.0
Unvested restricted share participation	(0.6)	(1.3)	(2.4)	(3.6)
Net income attributable to Trinity Industries, Inc. – basic	$ 27.1	$ 65.6	$ 129.6	$ 160.4
Net income attributable to Trinity Industries, Inc. - basic, Average Shares (in shares)	145.0	148.0	146.1	148.6
Net income attributable to Trinity Industries, Inc. - basic, EPS (in dollars per share)	$ 0.19	$ 0.44	$ 0.89	$ 1.08
Effect of dilutive securities:
Nonparticipating unvested restricted shares and stock options, Income (Loss)	$ 0.0	$ 0.0	$ 0.0	$ 0.0
Nonparticipating unvested restricted shares and stock options, average shares	0.8	0.5	0.9	0.4
Convertible subordinated notes, Income (Loss)	$ 0.0	$ 0.0	$ 0.0	$ 0.0
Convertible subordinated notes, Average Shares	0.0	2.8	1.8	2.1
Net income attributable to Trinity Industries, Inc. – diluted	$ 27.1	$ 65.6	$ 129.6	$ 160.4
Net income attributable to Trinity Industries, Inc. - diluted, Average Shares	145.8	151.3	148.8	151.1
Net income attributable to Trinity Industries, Inc. - diluted, EPS (in dollars per share)	$ 0.19	$ 0.43	$ 0.87	$ 1.06