Summary of Significant Accounting Policies - ASU 2014-09 Adoption (Details) - USD ($) $ in Millions		3 Months Ended			9 Months Ended
		Sep. 30, 2018		Sep. 30, 2017	Sep. 30, 2018		Sep. 30, 2017	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenues		$ 930.9		$ 973.6	$ 2,704.5		$ 2,756.4
Cost of revenues		752.0		722.7	2,100.2		2,065.2
Operating Profit (Loss)		78.9		152.4	303.0		402.9
Income before income taxes		39.0		107.6	181.5		271.4
Provision for income taxes		10.7		39.7	46.1		97.8
Net income		28.3		67.9	135.4		173.6
Net income attributable to Trinity Industries, Inc.		27.7		66.9	132.0		164.0
Receivables, net of allowance		396.2	[1]		396.2	[1]		$ 369.7
Raw materials and supplies		376.6	[1]		376.6	[1]		296.7
Work in process		182.2	[1]		182.2	[1]		179.0
Finished goods		148.2	[1]		148.2	[1]		164.9
Accrued liabilities		411.0	[1]		411.0	[1]		440.0
Deferred income taxes		755.9	[1]		755.9	[1]		743.2
Retained earnings		4,212.1	[1]		4,212.1	[1]		$ 4,123.4
Provision for deferred income taxes					57.8		151.7
(Increase) decrease in receivables					(23.5)		(94.3)
(Increase) decrease in inventories					(110.1)		10.6
Increase (decrease) in accrued liabilities					(14.7)		12.5
Net cash provided (required) by operating activities					319.9		488.2
Accounting Standards Update 2014-09 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating Profit (Loss)		(2.6)			1.0
Income before income taxes		(2.6)			1.0
Provision for income taxes		(0.6)			0.2
Net income		(2.0)			0.8
Net income attributable to Trinity Industries, Inc.		(2.0)			0.8
Receivables, net of allowance	[1]	(16.1)			(16.1)
Raw materials and supplies	[1]	0.0			0.0
Work in process	[1]	17.1			17.1
Finished goods	[1]	5.4			5.4
Accrued liabilities	[1]	(0.1)			(0.1)
Deferred income taxes	[1]	1.5			1.5
Retained earnings	[1]	5.0			5.0
Provision for deferred income taxes					0.2
(Increase) decrease in receivables					8.3
(Increase) decrease in inventories					5.4
Increase (decrease) in accrued liabilities					(14.7)
Net cash provided (required) by operating activities					0.0
Balance without adjustment for ASU 2014-09 [Domain]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating Profit (Loss)		76.3			304.0
Income before income taxes		36.4			182.5
Provision for income taxes		10.1			46.3
Net income		26.3			136.2
Net income attributable to Trinity Industries, Inc.		25.7			132.8
Receivables, net of allowance	[1]	380.1			380.1
Raw materials and supplies	[1]	376.6			376.6
Work in process	[1]	199.3			199.3
Finished goods	[1]	153.6			153.6
Accrued liabilities	[1]	410.9			410.9
Deferred income taxes	[1]	757.4			757.4
Retained earnings	[1]	4,217.1			4,217.1
Provision for deferred income taxes					58.0
(Increase) decrease in receivables					(15.2)
(Increase) decrease in inventories					(104.7)
Increase (decrease) in accrued liabilities					(29.4)
Net cash provided (required) by operating activities					319.9
Manufacturing
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenues		703.7		698.7	2,089.8		2,111.0
Cost of revenues		619.0		$ 566.1	1,755.3		$ 1,732.8
Manufacturing | Accounting Standards Update 2014-09 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenues		(8.3)			6.4
Cost of revenues		(5.7)			5.4
Manufacturing | Balance without adjustment for ASU 2014-09 [Domain]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenues		695.4			2,096.2
Cost of revenues		$ 613.3			$ 1,760.7

[1] (unaudited)