Consolidated Statement of Stockholders' Equity (unaudited) - 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
Common Stock, Shares, Issued		(133,300,000)				(100,000)
Common Stock, Dividends, Per Share, Declared	$ 0.17
Beginning balance at Dec. 31, 2018	$ 2,562.0	$ 1.3	$ 1.2	$ 2,326.1	$ (116.8)	$ (1.0)	$ 2,210.8	$ 351.2
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	30.1			30.6			30.6	(0.5)
Other comprehensive (loss) income	(3.8)				(4.1)		(4.1)	0.3
Dividends, Common Stock, Cash	(22.3)			(22.3)			(22.3)
Stock-based compensation	$ 5.5		$ 5.5				5.5
Restricted shares, net, (in shares)						0
Shares repurchased, shares	(866,715)		(2,600,000)			(3,500,000)
Shares repurchased	$ (19.0)		$ (70.0)			$ (89.0)	(19.0)
Stock Issued During Period, Value, Restricted Stock Award, Net of Forfeitures	(0.5)		0.6			(1.1)	(0.5)
Distributions to noncontrolling interest	(0.4)						0.0	(0.4)
Cumulative Effect on Retained Earnings, Net of Tax	13.7			13.7			13.7
Stockholders' equity, other	0.2			(0.2)			(0.2)
Ending balance at Mar. 31, 2019	$ 2,565.1	$ 1.3	77.3	2,347.9	(120.9)	$ (91.1)	2,214.5	350.6
Common Stock, Shares, Issued		(133,300,000)				(3,600,000)
Common Stock, Shares, Issued		(119,700,000)				100,000
Stockholders' Equity Note, Spinoff Transaction				161.7
Common Stock, Dividends, Per Share, Declared	$ 0.19
Beginning balance at Dec. 31, 2019	$ 2,378.9	$ 1.2	0.0	2,182.9	(153.1)	$ (0.9)	2,030.1	348.8
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	162.3						161.7	0.6
Other comprehensive (loss) income	(23.2)				(23.5)		(23.5)	0.3
Dividends, Common Stock, Cash	(24.6)			(24.6)			(24.6)
Stock-based compensation	7.3		7.3				7.3
Restricted shares, net, (in shares)						0
Shares repurchased, shares						(1,850,000)
Shares repurchased	(35.4)					$ (35.4)	(35.4)
Stock Issued During Period, Value, Restricted Stock Award, Net of Forfeitures	(0.2)		0.7			(0.9)	(0.2)
Cumulative Effect on Retained Earnings, Net of Tax	0.5			0.5			0.5
Stockholders' equity, other	(0.5)			0.5			0.5
Ending balance at Mar. 31, 2020	$ 2,466.1	$ 1.2	$ 8.0	$ 2,321.0	$ (176.6)	$ (37.2)	$ 2,116.4	$ 349.7
Common Stock, Shares, Issued		(119,700,000)				2,000,000.0