Revenues and Gross Profit - Total Revenues and Gross Profit by Product Line (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Product Information [Line Items]
Total revenues	$ 1,321.4	$ 1,420.2	$ 3,550.3	$ 3,638.7
Gross profit (loss)	404.5	420.6	927.4	920.4
Interproduct Revenues
Product Information [Line Items]
Total revenues	(81.4)	(77.3)	(210.9)	(203.6)
Corporate
Product Information [Line Items]
Gross profit (loss)	0.7	1.7	4.3	1.4
Building Materials Business
Product Information [Line Items]
Total revenues	1,260.5	1,355.4	3,370.1	3,423.5
Building Materials Business | Operating Segments
Product Information [Line Items]
Total revenues	1,260.5	1,355.4	3,370.1	3,423.5
Gross profit (loss)	383.8	395.9	861.0	842.4
Building Materials Business | Operating Segments | Products and Services
Product Information [Line Items]
Total revenues	1,185.5	1,263.9	3,157.2	3,198.7
Gross profit (loss)	382.9	395.7	860.7	842.0
Magnesia Specialties | Operating Segments
Product Information [Line Items]
Total revenues	60.9	64.8	180.2	215.2
Gross profit (loss)	20.0	23.0	62.1	76.6
Magnesia Specialties | Operating Segments | Products and Services
Product Information [Line Items]
Total revenues	55.2	59.3	164.0	198.9
Gross profit (loss)	21.0	24.0	65.3	79.8
Aggregates | Building Materials Business | Operating Segments | Reportable Subsegments | Products and Services
Product Information [Line Items]
Total revenues	766.9	818.7	2,092.1	2,121.4
Gross profit (loss)	279.1	287.1	640.4	636.5
Cement | Building Materials Business | Operating Segments | Reportable Subsegments | Products and Services
Product Information [Line Items]
Total revenues	115.6	119.6	331.7	331.0
Gross profit (loss)	46.5	48.5	117.2	104.5
Ready Mixed Concrete | Building Materials Business | Operating Segments | Reportable Subsegments | Products and Services
Product Information [Line Items]
Total revenues	254.6	271.8	689.4	724.2
Gross profit (loss)	24.7	29.0	56.7	62.5
Asphalt and Paving | Building Materials Business | Operating Segments | Reportable Subsegments | Products and Services
Product Information [Line Items]
Total revenues	129.8	131.1	254.9	225.7
Gross profit (loss)	32.6	31.1	46.4	38.5
Freight
Product Information [Line Items]
Total revenues	80.7	97.0	229.1	241.1
Freight | Building Materials Business
Product Information [Line Items]
Total revenues	75.0	91.5	212.9	224.8
Freight | Building Materials Business | Operating Segments
Product Information [Line Items]
Total revenues	75.0	91.5	212.9	224.8
Gross profit (loss)	0.9	0.2	0.3	0.4
Freight | Magnesia Specialties | Operating Segments
Product Information [Line Items]
Total revenues	5.7	5.5	16.2	16.3
Gross profit (loss)	$ (1.0)	$ (1.0)	$ (3.2)	$ (3.2)