Consolidated Statement of Stockholders' Equity (Unaudited) (USD $) In Millions, except Share data	Total	Common Stock	Capital in Excess of Par Value	Retained Earnings	Accumulated Other Comprehensive Loss	Treasury Stock	Trinity Stockholders' Equity	Noncontrolling Interest
Beginning Balance at Dec. 31, 2011	$ 1,948.3	$ 81.7	$ 626.5	$ 1,314.7	$ (134.0)	$ (25.1)	$ 1,863.8	$ 84.5
Beginning Balance, Shares at Dec. 31, 2011		81,700,000				(1,500,000)
Net income	119.8			120.7			120.7	(0.9)
Other comprehensive income	6.3				5.6		5.6	0.7
Cash dividends on common stock	(16.0)			(16.0)			(16.0)
Restricted shares issued, net	9.4		10.7			(1.3)	9.4
Restricted shares issued, net, Shares						400,000
Shares repurchased	(41.2)					(41.2)	(41.2)
Shares repurchased, Shares	(1,692,229)					(1,700,000)
Stock options exercised	1.4		0.7			0.7	1.4
Stock options exercised, Shares						100,000
Stock-based compensation expense	0.2		0.2				0.2
Ending Balance at Jun. 30, 2012	$ 2,028.2	$ 81.7	$ 638.1	$ 1,419.4	$ (128.4)	$ (66.9)	$ 1,943.9	$ 84.3
Ending Balance, Shares at Jun. 30, 2012		81,700,000				(2,700,000)