Revenue Recognition - Schedule of Company's Total Revenues by Category for each Reportable Segment (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Revenue Recognition [Line Items]
Total	$ 1,321.4	$ 1,420.2	$ 3,550.3	$ 3,638.7
Building Materials Business
Revenue Recognition [Line Items]
Total	1,260.5	1,355.4	3,370.1	3,423.5
Products and Services
Revenue Recognition [Line Items]
Total	1,240.7	1,323.2	3,321.2	3,397.6
Products and Services | Building Materials Business
Revenue Recognition [Line Items]
Total	1,185.5	1,263.9	3,157.2	3,198.7
Freight
Revenue Recognition [Line Items]
Total	80.7	97.0	229.1	241.1
Freight | Building Materials Business
Revenue Recognition [Line Items]
Total	75.0	91.5	212.9	224.8
Operating Segments | Building Materials Business East Group
Revenue Recognition [Line Items]
Total	549.3	582.0	1,465.9	1,500.8
Operating Segments | Building Materials Business West Group
Revenue Recognition [Line Items]
Total	711.2	773.4	1,904.2	1,922.7
Operating Segments | Building Materials Business
Revenue Recognition [Line Items]
Total	1,260.5	1,355.4	3,370.1	3,423.5
Operating Segments | Magnesia Specialties
Revenue Recognition [Line Items]
Total	60.9	64.8	180.2	215.2
Operating Segments | Products and Services | Building Materials Business East Group
Revenue Recognition [Line Items]
Total	514.1	539.8	1,371.8	1,398.6
Operating Segments | Products and Services | Building Materials Business West Group
Revenue Recognition [Line Items]
Total	671.4	724.1	1,785.4	1,800.1
Operating Segments | Products and Services | Magnesia Specialties
Revenue Recognition [Line Items]
Total	55.2	59.3	164.0	198.9
Operating Segments | Freight | Building Materials Business East Group
Revenue Recognition [Line Items]
Total	35.2	42.2	94.1	102.2
Operating Segments | Freight | Building Materials Business West Group
Revenue Recognition [Line Items]
Total	39.8	49.3	118.8	122.6
Operating Segments | Freight | Building Materials Business
Revenue Recognition [Line Items]
Total	75.0	91.5	212.9	224.8
Operating Segments | Freight | Magnesia Specialties
Revenue Recognition [Line Items]
Total	$ 5.7	$ 5.5	$ 16.2	$ 16.3