Earnings Per Common Share - Computation of basic and diluted net income attributable to Trinity Industries, Inc. (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	$ (0.3)	$ (0.2)	$ 28.2	$ 26.4	$ 8.1	$ 31.1	$ 31.9	$ 32.3	$ 54.1	$ 103.4	$ 161.5
Undistributed Discontinued Operation Earnings (Loss), Allocation to Participating Securities, Basic									(0.6)	(1.9)	(3.6)
Net Income (Loss) from Discontinued Operations Available to Common Shareholders, Basic									$ 53.5	$ 101.5	$ 157.9
Total weighted average restricted shares and antidilutive stock options									5.8	6.4	6.6
Earnings Per Share Reconciliation [Abstract]
Net income from continuing operations	$ 27.7	$ 28.3	$ 65.5	$ 41.6	$ 540.0	$ 67.9	$ 54.0	$ 51.7	$ 163.1	$ 713.6	$ 364.7
Net income attributable to noncontrolling interest									3.8	11.1	21.1
Net income attributable to Trinity Industries, Inc.									105.2	599.1	182.1
Unvested restricted share participation									(2.2)	(13.5)	(5.8)
Net income from continuing operations attributable to Trinity Industries, Inc. – basic									$ 103.0	$ 585.6	$ 176.3
Net income attributable to Trinity Industries, Inc. - basic (shares)									144.0	148.6	148.4
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Basic Share	$ 0.00	$ 0.00	$ 0.19	$ 0.18	$ 0.05	$ 0.21	$ 0.21	$ 0.21	$ 0.37	$ 0.68	$ 1.06
Net income attributable to Trinity Industries, Inc. - basic (EPS)	0.20	0.19	0.43	0.27	3.56	0.44	0.34	0.30	$ 1.09	$ 4.62	$ 2.25
Incremental Weighted Average Shares Attributable to Dilutive Effect [Abstract]
Stock options									$ 0.0	$ 0.0	$ 0.0
Stock options (shares)									1.0	0.5	0.0
Convertible subordinated notes									$ 0.0	$ 0.3	$ 0.0
Convertible subordinated notes (shares)									1.4	2.9	0.2
Net Income (Loss) from Discontinued Operations Available to Common Shareholders, Diluted									$ 53.5	$ 101.5	$ 157.9
Net income from continuing operations attributable to Trinity Industries, Inc. – diluted									$ 103.0	$ 585.9	$ 176.3
Net income attributable to Trinity Industries, Inc - diluted (shares)									146.4	152.0	148.6
Net income attributable to Trinity Industries, Inc. - diluted (EPS)	0.19	0.19	0.43	0.26	3.42	0.43	0.33	0.30	$ 1.07	$ 4.52	$ 2.25
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Diluted Share	$ 0.00	$ 0.00	$ 0.19	$ 0.17	$ 0.05	$ 0.20	$ 0.21	$ 0.21	$ 0.37	$ 0.67	$ 1.06