Revenue Recognition - Schedule of Company's Total Revenues by Category for each Reportable Segment (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenue Recognition [Line Items]
Total	$ 4,729.9	$ 4,739.1	$ 4,244.3
Building Materials Business
Revenue Recognition [Line Items]
Total	4,487.2	4,467.8	3,956.6
Operating Segments | Building Materials Business East Group
Revenue Recognition [Line Items]
Total	1,949.1	1,949.0	1,643.1
Operating Segments | Building Materials Business West Group
Revenue Recognition [Line Items]
Total	2,538.1	2,518.8	2,313.5
Operating Segments | Building Materials Business
Revenue Recognition [Line Items]
Total	4,487.2	4,467.8	3,956.6
Operating Segments | Magnesia Specialties
Revenue Recognition [Line Items]
Total	242.7	271.3	287.7
Products and Services
Revenue Recognition [Line Items]
Total	4,432.1	4,422.3	3,980.4
Products and Services | Building Materials Business
Revenue Recognition [Line Items]
Total	4,211.2	4,172.4	3,711.8
Products and Services | Operating Segments | Building Materials Business East Group
Revenue Recognition [Line Items]
Total	1,826.6	1,814.5	1,539.8
Products and Services | Operating Segments | Building Materials Business West Group
Revenue Recognition [Line Items]
Total	2,384.6	2,357.9	2,172.0
Products and Services | Operating Segments | Magnesia Specialties
Revenue Recognition [Line Items]
Total	220.9	249.9	268.6
Freight
Revenue Recognition [Line Items]
Total	297.8	316.8	263.9
Freight | Building Materials Business
Revenue Recognition [Line Items]
Total	276.0	295.4	244.8
Freight | Operating Segments | Building Materials Business East Group
Revenue Recognition [Line Items]
Total	122.5	134.5	103.3
Freight | Operating Segments | Building Materials Business West Group
Revenue Recognition [Line Items]
Total	153.5	160.9	141.5
Freight | Operating Segments | Building Materials Business
Revenue Recognition [Line Items]
Total	276.0	295.4	244.8
Freight | Operating Segments | Magnesia Specialties
Revenue Recognition [Line Items]
Total	$ 21.8	$ 21.4	$ 19.1