Consolidated Statement of Stockholders' Equity (unaudited) (USD $) In Millions, except Share data, unless otherwise specified	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, 2014	$ 3,397.4		$ 155.7	$ 463.2	$ 2,489.9	$ (111.9)	$ (1.0)	$ 2,995.9	$ 401.5
Beginning balance, Shares at Dec. 31, 2014			155,700,000				(100,000)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	189.0				180.2			180.2	8.8
Other comprehensive income (loss)	0.5					(0.1)		(0.1)	0.6
Cash dividends on common stock	(15.6)				(15.6)			(15.6)
Restricted shares, net	16.0			16.6			(0.6)	16.0
Restricted shares, net, Shares							0
Shares repurchased	(25.0)						(25.0)	(25.0)
Shares repurchased, Shares							(700,000)
Excess tax benefits from stock-based compensation	0.4			0.4				0.4
Distributions to noncontrolling interest	(11.3)								(11.3)
Ending balance at Mar. 31, 2015	$ 3,551.4	[1]	$ 155.7	$ 480.2	$ 2,654.5	$ (112.0)	$ (26.6)	$ 3,151.8	$ 399.6
Ending balance, Shares at Mar. 31, 2015			155,700,000				(800,000)

[1] (unaudited)