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)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, 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)
Share-based Payment Arrangement, Expense	$ 5.5		5.5				5.5
Stock Issued During Period, Shares, Restricted Stock Award, Net of Forfeitures						0
Treasury Stock, Shares, Acquired	(866,715)					(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)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, 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
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Dividends, Per Share, Declared	$ 0.17
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, 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	66.9
Other comprehensive (loss) income	(10.0)
Share-based Payment Arrangement, Expense	13.0
Treasury Stock, Shares, Acquired			(2,600,000)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Ending Balance at Jun. 30, 2019	$ 2,529.6	$ 1.3	$ 0.0	2,305.8	(127.4)	$ (0.9)	2,178.8	350.8
Common Stock, Shares, Issued		(133,300,000)				(3,600,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Par or Stated Value Per Share	$ 0.01
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Beginning Balance at Mar. 31, 2019	$ 2,565.1	$ 1.3	77.3	2,347.9	(120.9)	$ (91.1)	2,214.5	350.6
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	36.8			36.4			36.4	0.4
Other comprehensive (loss) income	(6.2)				(6.5)		(6.5)	0.3
Dividends, Common Stock, Cash	(21.6)			(21.6)			(21.6)
Share-based Payment Arrangement, Expense	7.5		7.5				7.5
Stock Issued During Period, Shares, Restricted Stock Award, Net of Forfeitures						500,000
Treasury Stock, Shares, Acquired						(2,133,116)
Shares repurchased	(44.0)		0.0			$ (44.0)	(44.0)
Stock Issued During Period, Value, Restricted Stock Award, Net of Forfeitures	(7.5)	$ 0.7	1.0			$ (8.5)	(7.5)
Distributions to noncontrolling interest	(0.5)						0.0	(0.5)
Treasury Stock, Shares, Retired		6,100,000				6,100,000
Treasury Stock, Retired, Cost Method, Amount	0.0		(85.8)	(56.9)		$ (142.7)	0.0
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Ending Balance at Jun. 30, 2019	$ 2,529.6	$ 1.3	0.0	2,305.8	(127.4)	$ (0.9)	2,178.8	350.8
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Dividends, Per Share, Declared	$ 0.17
Common Stock, Shares, Issued		(127,900,000)				(100,000)
Common Stock, Par or Stated Value Per Share	$ 0.01
Common Stock, Shares, Issued		(119,700,000)				100,000
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, 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			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)
Share-based Payment Arrangement, Expense	7.3		7.3				7.3
Stock Issued During Period, Shares, Restricted Stock Award, Net of Forfeitures						0
Treasury Stock, Shares, Acquired						(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
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, 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
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Dividends, Per Share, Declared	$ 0.19
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, 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	(125.5)
Other comprehensive (loss) income	(18.6)							0.6
Share-based Payment Arrangement, Expense	14.9
Cumulative Effect on Retained Earnings, Net of Tax	0.5
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Ending Balance at Jun. 30, 2020	$ 2,160.4	$ 1.2	0.0	2,063.3	(172.3)	$ (0.9)	1,891.3	269.1
Common Stock, Shares, Issued		(119,700,000)				2,000,000.0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Par or Stated Value Per Share	$ 0.01
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Beginning Balance at Mar. 31, 2020	$ 2,466.1	$ 1.2	8.0	2,321.0	(176.6)	$ (37.2)	2,116.4	349.7
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	(287.8)			(206.9)			(206.9)	(80.9)
Other comprehensive (loss) income	4.6				4.3		4.3	0.3
Dividends, Common Stock, Cash	(20.6)			(20.6)			(20.6)
Share-based Payment Arrangement, Expense	7.6		7.6				7.6
Stock Issued During Period, Shares, Restricted Stock Award, Net of Forfeitures		1,500,000				600,000
Treasury Stock, Shares, Acquired						0
Shares repurchased						$ 0.0
Stock Issued During Period, Value, Restricted Stock Award, Net of Forfeitures	(9.5)		1.9			$ (11.4)	(9.5)
Treasury Stock, Shares, Retired		2,500,000				2,500,000
Treasury Stock, Retired, Cost Method, Amount	0.0		(17.5)	(30.2)		$ (47.7)	0.0
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Ending Balance at Jun. 30, 2020	$ 2,160.4	$ 1.2	$ 0.0	$ 2,063.3	$ (172.3)	$ (0.9)	$ 1,891.3	$ 269.1
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common Stock, Dividends, Per Share, Declared	$ 0.19
Common Stock, Shares, Issued		(118,700,000)				100,000
Common Stock, Par or Stated Value Per Share	$ 0.01