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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

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