Consolidated Statement of Stockholders' Equity (unaudited) - 3 months ended Mar. 31, 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	41.6				40.2			40.2	1.4
Other comprehensive income	1.9					1.5		1.5	0.4
Cash dividends on common stock	(19.4)				(19.4)			(19.4)
Restricted shares, net, (in shares)							(100,000)
Restricted shares, net	$ 8.2			10.1			$ (1.9)	8.2
Shares repurchased (in shares)	1,519,503						(1,500,000)
Shares repurchased	$ (50.0)						$ (50.0)	(50.0)
Stock options exercised	0.1			0.1				0.1
Distributions to noncontrolling interest	(5.8)							0.0	(5.8)
Ending balance (in shares) at Mar. 31, 2018			150,900,000				(1,700,000)
Ending balance at Mar. 31, 2018	$ 4,830.6	[1]	$ 1.6	$ 492.7	$ 4,158.9	$ (122.0)	$ (53.5)	$ 4,477.7	$ 352.9

[1] (unaudited)