Business Segments - Financial Data for Continuing Operations for Company's Reportable Business Segments (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Segment Reporting Information [Line Items]
Total revenues	$ 1,321.4	$ 1,420.2	$ 3,550.3	$ 3,638.7
Earnings (Loss) from operations	400.6	345.3	764.8	700.4
Assets employed	10,435.4		10,435.4		$ 10,131.6
Products and Services
Segment Reporting Information [Line Items]
Total revenues	1,240.7	1,323.2	3,321.2	3,397.6
Building Materials Business
Segment Reporting Information [Line Items]
Total revenues	1,260.5	1,355.4	3,370.1	3,423.5
Earnings (Loss) from operations	393.7	347.6	754.3	704.2
Assets employed	9,764.2		9,764.2		9,642.5
Building Materials Business | Products and Services
Segment Reporting Information [Line Items]
Total revenues	1,185.5	1,263.9	3,157.2	3,198.7
Operating Segments | Building Materials Business East Group
Segment Reporting Information [Line Items]
Total revenues	549.3	582.0	1,465.9	1,500.8
Earnings (Loss) from operations	181.4	190.8	386.1	416.5
Assets employed	4,373.9		4,373.9		4,320.6
Operating Segments | Building Materials Business East Group | Products and Services
Segment Reporting Information [Line Items]
Total revenues	514.1	539.8	1,371.8	1,398.6
Operating Segments | Magnesia Specialties
Segment Reporting Information [Line Items]
Total revenues	60.9	64.8	180.2	215.2
Earnings (Loss) from operations	16.4	20.1	51.2	68.0
Assets employed	163.5		163.5		176.2
Operating Segments | Magnesia Specialties | Products and Services
Segment Reporting Information [Line Items]
Total revenues	55.2	59.3	164.0	198.9
Operating Segments | Building Materials Business
Segment Reporting Information [Line Items]
Total revenues	1,260.5	1,355.4	3,370.1	3,423.5
Operating Segments | Building Materials Business West Group
Segment Reporting Information [Line Items]
Total revenues	711.2	773.4	1,904.2	1,922.7
Earnings (Loss) from operations	212.3	156.8	368.2	287.7
Assets employed	5,390.3		5,390.3		5,321.9
Operating Segments | Building Materials Business West Group | Products and Services
Segment Reporting Information [Line Items]
Total revenues	671.4	724.1	1,785.4	1,800.1
Corporate
Segment Reporting Information [Line Items]
Earnings (Loss) from operations	(9.5)	$ (22.4)	(40.7)	$ (71.8)
Assets employed	$ 507.7		$ 507.7		$ 312.9