Consolidated Statements of Stockholders' Equity - USD ($) $ in Millions	Total	Common Stock	Capital in Excess of Par Value	Retained Earnings	Accumulated Other Comprehensive Loss	Treasury Stock	Trinity Stockholders’ Equity	Noncontrolling Interest
Net Income (Loss) Attributable to Parent	$ 343.6
Beginning balance at Dec. 31, 2015	4,048.7	$ 1.5	$ 548.5	$ 3,220.3	$ (115.4)	$ (1.0)	$ 3,653.9	$ 394.8
Beginning balance, shares at Dec. 31, 2015		(152,900,000)				(100,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	364.7			343.6			343.6	21.1
Other comprehensive income	5.0				1.9		1.9	3.1
Cash dividends on common stock	(66.6)			(66.6)			(66.6)
Restricted shares, net	25.0	$ 0.1	46.2			$ (21.3)	25.0
Restricted shares, net, shares		2,600,000				(1,200,000)
Shares repurchased	(34.7)					$ (34.7)	(34.7)
Shares repurchased, shares						(2,100,000)
Excess net tax deficiency from stock-based compensation	(4.5)		(4.5)				(4.5)
Distributions to noncontrolling interest	(26.4)						0.0	(26.4)
Retirement of treasury stock	0.0	$ 0.0	(56.0)			$ (56.0)	0.0
Retirement of treasury stock, shares		(3,300,000)				(3,300,000)
Other	(0.1)		0.4	0.0		$ (0.5)	(0.1)
Ending balance at Dec. 31, 2016	4,311.1	$ 1.6	534.6	3,497.3	(113.5)	$ (1.5)	3,918.5	392.6
Ending balance, shares at Dec. 31, 2016		(152,200,000)				(100,000)
Net Income (Loss) Attributable to Parent	702.5
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	713.6			702.5			702.5	11.1
Other comprehensive income	11.3				8.7		8.7	2.6
Cash dividends on common stock	(75.8)			(75.8)			(75.8)
Restricted shares, net	16.7	$ 0.0	35.2			$ (18.5)	16.7
Restricted shares, net, shares		1,700,000				(700,000)
Shares repurchased	$ (85.4)					$ (85.4)	(85.4)
Shares repurchased, shares	(2,825,400)					(2,800,000)
Stock options exercised	$ 0.2	$ 0.0	0.2			$ 0.0	0.2
Stock options exercised, shares		0				0
Distributions to noncontrolling interest	(48.7)						0.0	(48.7)
Retirement of treasury stock	0.0	$ 0.0	(103.8)			$ (103.8)	0.0
Stock issued for acquisition (shares)		500,000
Stock issued for acquisition (value)	14.7		14.7				14.7
Retirement of treasury stock, shares		(3,500,000)				(3,500,000)
Other	0.3		1.6	(0.6)		$ 0.0	1.0	(0.7)
Ending balance at Dec. 31, 2017	4,858.0	$ 1.6	482.5	4,123.4	(104.8)	$ (1.6)	4,501.1	356.9
Ending balance, shares at Dec. 31, 2017		(150,900,000)				(100,000)
CumulativeEffectofNewAccountingPrincipleinPeriodofAdoption(Duration)	0.0			18.7	(18.7)		0.0
Net Income (Loss) Attributable to Parent	159.3
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	163.1						159.3	3.8
Other comprehensive income	(13.2)				(14.6)		(14.6)	1.4
Cash dividends on common stock	(75.9)			(75.9)			(75.9)
Restricted shares, net	25.0	$ 0.0	44.4			$ (19.4)	25.0
Restricted shares, net, shares		(200,000)				600,000
Shares repurchased	$ (500.1)		75.9	145.9		$ 430.1	(500.1)
Shares repurchased, shares	(17,206,643)					(17,200,000)
Stock options exercised	$ 0.3	$ 0.0	0.3			$ 0.0	0.3
Stock options exercised, shares	34,343	0				0
Distributions to noncontrolling interest	$ (10.9)						0.0	(10.9)
Retirement of treasury stock	0.0	$ (0.2)	(449.3)			$ (449.5)	0.0
Adjustments to Additional Paid in Capital, Convertible Debt with Conversion Feature	(152.9)		(152.9)				(152.9)
Stockholders' Equity Note, Spinoff Transaction	(1,732.2)			(1,753.5)	21.3		(1,732.2)
Retirement of treasury stock, shares		(17,800,000)				(17,800,000)
Other	0.8	$ (0.1)	0.3	0.0		$ 0.6	0.8	0.0
Ending balance at Dec. 31, 2018	$ 2,562.0	$ 1.3	$ 1.2	$ 2,326.1	$ (116.8)	$ (1.0)	$ 2,210.8	$ 351.2
Ending balance, shares at Dec. 31, 2018		(133,300,000)				(100,000)