Earnings Per Common Share - EPS calculation (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Weighted Average Number of Shares Outstanding, Basic and Diluted			5.5	5.9
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	1.2		0.2	0.0
Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	$ 48.1	$ 28.5	$ 116.9	$ 81.0
Net Income (Loss) Attributable to Noncontrolling Interest	1.3	(0.6)	1.4	(3.4)
Unvested restricted share participation	(0.6)	(0.6)	(1.6)	(1.9)
Net Income (Loss) from Continuing Operations Available to Common Shareholders, Basic	48.8	27.3	116.7	75.7
Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	(0.4)	(0.2)	(2.3)	54.4
Undistributed Discontinued Operation Earnings (Loss), Allocation to Participating Securities, Basic	0.0	0.0	0.0	(0.5)
Net Income (Loss) from Discontinued Operations Available to Common Shareholders, Basic	(0.4)	(0.2)	(2.3)	53.9
Net Income (Loss) Available to Common Stockholders	$ 48.4	$ 27.1	$ 114.4	$ 129.6
Income (Loss) from Continuing Operations, Per Basic Share	$ 0.39	$ 0.19	$ 0.91	$ 0.52
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Basic Share	0	0	(0.02)	0.37
Net income attributable to Trinity Industries, Inc. - basic, EPS (in dollars per share)	0.39	0.19	0.89	0.89
Income (Loss) from Continuing Operations, Per Diluted Share	0.39	0.19	0.90	0.51
Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Diluted Share	0	0	(0.02)	0.36
Net income attributable to Trinity Industries, Inc. - diluted, EPS (in dollars per share)	$ 0.39	$ 0.19	$ 0.88	$ 0.87
Computation of basic and diluted net income attributable to Trinity Industries, Inc
Net income attributable to Trinity Industries, Inc. - basic, Average Shares (in shares)	124.7	145.0	127.6	146.1
Effect of dilutive securities:
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	1.3	0.8	1.6	0.9
Incremental Common Shares Attributable to Dilutive Effect of Conversion of Debt Securities, Treasury Stock Method	0.0	0.0	0.0	1.8
Net income attributable to Trinity Industries, Inc. - diluted, Average Shares	126.0	145.8	129.2	148.8