Consolidated Statements of Stockholders' Equity - USD ($) shares in Millions, $ in Millions	Total	Cumulative Effect, Period of Adoption, Adjustment [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]		Retained Earnings [Member] Cumulative Effect, Period of Adoption, Adjustment [Member]	AOCI Attributable to Parent [Member]	AOCI Attributable to Parent [Member] Cumulative Effect, Period of Adoption, Adjustment [Member]	Treasury Stock [Member]	Parent [Member]	Parent [Member] Cumulative Effect, Period of Adoption, Adjustment [Member]	Noncontrolling Interest [Member]
Common Stock, Shares, Issued			(150.9)							(0.1)
Total stockholders' equity	$ 4,858.0		$ 1.6	$ 482.5	$ 4,123.4			$ (104.8)		$ (1.6)	$ 4,501.1		$ 356.9
Net income (loss)	163.1				159.3						159.3		3.8
Other comprehensive income (loss):	(13.2)							(14.6)			(14.6)		1.4
Dividends, Common Stock, Cash	(75.9)				(75.9)	[1]					(75.9)
Stock-based compensation expense	29.3			29.3							29.3
Shares repurchased										(17.2)
Shares repurchased	(500.1)			(75.9)	(145.9)					$ (430.1)	(500.1)
Settlement of share-based awards, net			(0.2)							(0.6)
Settlement of share-based awards, net	4.3			(15.1)						$ 19.4	4.3
Stock options exercised	0.3			0.3							0.3
Retirement of treasury stock			17.8							17.8
Retirement of treasury stock	0.0		$ 0.2	(449.3)	0.0					$ (449.5)	0.0
Distributions to noncontrolling interest	(10.9)												(10.9)
Cumulative effect of adopting new accounting standards							$ 18.7		$ (18.7)
Redemption of convertible subordinated notes	152.9			152.9							152.9
Distribution of Arcosa, Inc.	1,732.2				1,753.5			(21.3)			1,732.2
Stockholders' Equity, Other	$ (0.8)		$ (0.1)	(0.3)						$ 0.6	0.8
Common Stock, Dividends, Per Share, Declared	$ 0.52
Common Stock, Shares, Issued			(133.3)							(0.1)
$0.01 Par Value	$ 0.01
Total stockholders' equity	$ 2,562.0		$ 1.3	1.2	2,326.1			(116.8)		$ (1.0)	2,210.8		351.2
Net income (loss)	136.1				137.6						137.6		(1.5)
Other comprehensive income (loss):	(35.0)							(36.3)			(36.3)		1.3
Dividends, Common Stock, Cash	(88.2)				(88.2)	[1]					(88.2)
Stock-based compensation expense	29.2			$ 29.2							29.2
Shares repurchased				(2.6)						(13.7)
Shares repurchased	(224.7)			$ (70.0)						$ (294.7)	(224.7)
Settlement of share-based awards, net			(0.7)							(0.6)
Settlement of share-based awards, net	8.5			(2.8)						$ 11.3	8.5
Retirement of treasury stock			14.3							14.3
Retirement of treasury stock	0.0		$ 0.1	(103.2)	(202.8)					$ (306.1)	0.0
Distributions to noncontrolling interest	(2.2)												(2.2)
Cumulative effect of adopting new accounting standards		$ 13.7					13.7					$ 13.7
Stockholders' Equity, Other	$ 3.5				(3.5)						(3.5)
Common Stock, Dividends, Per Share, Declared	$ 0.70
Common Stock, Shares, Issued			(119.7)							(0.1)
$0.01 Par Value	$ 0.01
Total stockholders' equity	$ 2,378.9		$ 1.2	0.0	2,182.9			(153.1)		$ (0.9)	2,030.1		348.8
Net income (loss)	(226.2)				(147.3)						(147.3)		(78.9)
Other comprehensive income (loss):	123.4							122.2			122.2		1.2
Dividends, Common Stock, Cash	(90.7)				(90.7)	[1]					(90.7)
Stock-based compensation expense	26.9			26.9							26.9
Shares repurchased										(9.3)
Shares repurchased	(193.1)									$ (193.1)	(193.1)
Settlement of share-based awards, net			(1.5)							(0.7)
Settlement of share-based awards, net	10.3			(3.6)						$ 13.9	10.3
Retirement of treasury stock			10.0							10.0
Retirement of treasury stock	0.0		$ 0.1	(30.5)	(176.5)					$ (207.1)	0.0
Contributions from noncontrolling interest	6.1												6.1
Cumulative effect of adopting new accounting standards		$ 0.5					$ 0.5					$ 0.5
Stockholders' Equity, Other	$ (0.5)				0.5						0.5
Common Stock, Dividends, Per Share, Declared	$ 0.78
Common Stock, Shares, Issued			(111.2)							(0.1)
$0.01 Par Value	$ 0.01
Total stockholders' equity	$ 2,016.0		$ 1.1	$ 0.0	$ 1,769.4			$ (30.9)		$ (0.8)	$ 1,738.8		$ 277.2

[1] Dividends of $0.78, $0.70, and $0.52 per common share for the years ended December 31, 2020, 2019, and 2018.