Consolidated Statement of Stockholders' Equity (unaudited) - 6 months ended Jun. 30, 2018 - 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
Beginning balance (in shares) at Dec. 31, 2017			(150,900,000)				(100,000)
Beginning balance at Dec. 31, 2017	$ 4,858.0		$ 1.6	$ 482.5	$ 4,123.4	$ (104.8)	$ (1.6)	$ 4,501.1	$ 356.9
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of new accounting principle	(4.0)				14.7	(18.7)		(4.0)
Net income	107.1				104.3			104.3	2.8
Other comprehensive income	1.4					0.6		0.6	0.8
Cash dividends on common stock	(39.0)				(39.0)			(39.0)
Restricted shares, net, (in shares)			(200,000)				(400,000)
Restricted shares, net	$ 7.6		$ 0.0	22.3			$ (14.7)	7.6
Shares repurchased, shares	(2,970,674)						(3,000,000)
Shares repurchased	$ (100.1)						$ (100.1)	(100.1)
Stock options exercised	0.1			0.1				0.1
Distributions to noncontrolling interest	(10.3)							0.0	(10.3)
Retirement of treasury stock - shares			3,400,000				3,400,000
Retirement of treasury stock - amount	0.0		$ 0.0	114.8			$ 114.8	0.0
Redemption of convertible subordinated notes	(152.9)			(152.9)				(152.9)
Stockholders' equity, other	(0.1)		$ (0.1)	0.0	0.0		$ 0.0	(0.1)	0.0
Ending balance (in shares) at Jun. 30, 2018			(147,700,000)				(100,000)
Ending balance at Jun. 30, 2018	$ 4,667.8	[1]	$ 1.5	$ 237.2	$ 4,203.4	$ (122.9)	$ (1.6)	$ 4,317.6	$ 350.2

[1] (unaudited)