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Revenues and Gross Profit - Total Revenues and Gross Profit by Product Line (Detail) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2020 | Sep. 30, 2019 | Sep. 30, 2020 | Sep. 30, 2019
Product Information [Line Items] |  |  |  |
Total revenues | $ 1,321.4 | $ 1,420.2 | $ 3,550.3 | $ 3,638.7
Gross profit (loss) | 404.5 | 420.6 | 927.4 | 920.4
Interproduct Revenues |  |  |  |
Product Information [Line Items] |  |  |  |
Total revenues | (81.4) | (77.3) | (210.9) | (203.6)
Corporate |  |  |  |
Product Information [Line Items] |  |  |  |
Gross profit (loss) | 0.7 | 1.7 | 4.3 | 1.4
Building Materials Business |  |  |  |
Product Information [Line Items] |  |  |  |
Total revenues | 1,260.5 | 1,355.4 | 3,370.1 | 3,423.5
Building Materials Business | Operating Segments |  |  |  |
Product Information [Line Items] |  |  |  |
Total revenues | 1,260.5 | 1,355.4 | 3,370.1 | 3,423.5
Gross profit (loss) | 383.8 | 395.9 | 861.0 | 842.4
Building Materials Business | Operating Segments | Products and Services |  |  |  |
Product Information [Line Items] |  |  |  |
Total revenues | 1,185.5 | 1,263.9 | 3,157.2 | 3,198.7
Gross profit (loss) | 382.9 | 395.7 | 860.7 | 842.0
Magnesia Specialties | Operating Segments |  |  |  |
Product Information [Line Items] |  |  |  |
Total revenues | 60.9 | 64.8 | 180.2 | 215.2
Gross profit (loss) | 20.0 | 23.0 | 62.1 | 76.6
Magnesia Specialties | Operating Segments | Products and Services |  |  |  |
Product Information [Line Items] |  |  |  |
Total revenues | 55.2 | 59.3 | 164.0 | 198.9
Gross profit (loss) | 21.0 | 24.0 | 65.3 | 79.8
Aggregates | Building Materials Business | Operating Segments | Reportable Subsegments | Products and Services |  |  |  |
Product Information [Line Items] |  |  |  |
Total revenues | 766.9 | 818.7 | 2,092.1 | 2,121.4
Gross profit (loss) | 279.1 | 287.1 | 640.4 | 636.5
Cement | Building Materials Business | Operating Segments | Reportable Subsegments | Products and Services |  |  |  |
Product Information [Line Items] |  |  |  |
Total revenues | 115.6 | 119.6 | 331.7 | 331.0
Gross profit (loss) | 46.5 | 48.5 | 117.2 | 104.5
Ready Mixed Concrete | Building Materials Business | Operating Segments | Reportable Subsegments | Products and Services |  |  |  |
Product Information [Line Items] |  |  |  |
Total revenues | 254.6 | 271.8 | 689.4 | 724.2
Gross profit (loss) | 24.7 | 29.0 | 56.7 | 62.5
Asphalt and Paving | Building Materials Business | Operating Segments | Reportable Subsegments | Products and Services |  |  |  |
Product Information [Line Items] |  |  |  |
Total revenues | 129.8 | 131.1 | 254.9 | 225.7
Gross profit (loss) | 32.6 | 31.1 | 46.4 | 38.5
Freight |  |  |  |
Product Information [Line Items] |  |  |  |
Total revenues | 80.7 | 97.0 | 229.1 | 241.1
Freight | Building Materials Business |  |  |  |
Product Information [Line Items] |  |  |  |
Total revenues | 75.0 | 91.5 | 212.9 | 224.8
Freight | Building Materials Business | Operating Segments |  |  |  |
Product Information [Line Items] |  |  |  |
Total revenues | 75.0 | 91.5 | 212.9 | 224.8
Gross profit (loss) | 0.9 | 0.2 | 0.3 | 0.4
Freight | Magnesia Specialties | Operating Segments |  |  |  |
Product Information [Line Items] |  |  |  |
Total revenues | 5.7 | 5.5 | 16.2 | 16.3
Gross profit (loss) | $ (1.0) | $ (1.0) | $ (3.2) | $ (3.2)

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