Revenues and Gross Profit - Total Revenues and Gross Profit by Product Line (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Product Information [Line Items]
Total revenues	$ 1,270.6	$ 1,279.5	$ 2,228.9	$ 2,218.4
Gross profit (loss)	380.5	356.9	522.9	499.8
Interproduct Revenues
Product Information [Line Items]
Total revenues	(75.9)	(67.8)	(129.5)	(126.1)
Corporate
Product Information [Line Items]
Gross profit (loss)	4.5	0.2	3.6	(0.3)
Building Materials Business
Product Information [Line Items]
Total revenues	1,217.0	1,203.2	2,109.6	2,068.1
Building Materials Business | Operating Segments
Product Information [Line Items]
Total revenues	1,217.0	1,203.2	2,109.6	2,068.1
Gross profit (loss)	359.1	328.6	477.2	446.5
Building Materials Business | Operating Segments | Products and Services
Product Information [Line Items]
Total revenues	1,140.6	1,125.7	1,971.7	1,934.9
Gross profit (loss)	359.4	328.4	477.8	446.4
Magnesia Specialties | Operating Segments
Product Information [Line Items]
Total revenues	53.6	76.3	119.3	150.3
Gross profit (loss)	16.9	28.1	42.1	53.6
Magnesia Specialties | Operating Segments | Products and Services
Product Information [Line Items]
Total revenues	48.9	70.4	108.8	139.5
Gross profit (loss)	18.2	29.2	44.3	55.8
Aggregates | Building Materials Business | Operating Segments | Reportable Subsegments | Products and Services
Product Information [Line Items]
Total revenues	754.9	757.8	1,325.2	1,302.7
Gross profit (loss)	268.0	251.5	361.3	349.5
Cement | Building Materials Business | Operating Segments | Reportable Subsegments | Products and Services
Product Information [Line Items]
Total revenues	109.5	112.3	216.1	211.4
Gross profit (loss)	43.4	42.2	70.7	56.0
Ready Mixed Concrete | Building Materials Business | Operating Segments | Reportable Subsegments | Products and Services
Product Information [Line Items]
Total revenues	245.1	241.2	434.8	452.3
Gross profit (loss)	26.1	19.0	32.0	33.5
Asphalt and Paving | Building Materials Business | Operating Segments | Reportable Subsegments | Products and Services
Product Information [Line Items]
Total revenues	107.0	82.2	125.1	94.6
Gross profit (loss)	21.9	15.7	13.8	7.4
Freight
Product Information [Line Items]
Total revenues	81.1	83.4	148.4	144.0
Freight | Building Materials Business
Product Information [Line Items]
Total revenues	76.4	77.5	137.9	133.2
Freight | Building Materials Business | Operating Segments
Product Information [Line Items]
Total revenues	76.4	77.5	137.9	133.2
Gross profit (loss)	(0.3)	0.2	(0.6)	0.1
Freight | Magnesia Specialties | Operating Segments
Product Information [Line Items]
Total revenues	4.7	5.9	10.5	10.8
Gross profit (loss)	$ (1.3)	$ (1.1)	$ (2.2)	$ (2.2)