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Post-Retirement Obligation - Summary of Principal Categories Percentage of Plan Assets (Detail) | Dec. 31, 2017 | Dec. 31, 2016
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Disclosure of fair value of plan assets [abstract] |  |
Shares in Brazilian companies | 6.63% | 3.84%
Fixed income securities | 74.12% | 74.96%
Real estate property | 8.05% | 8.14%
Others | 11.20% | 13.06%
Total | 100.00% | 100.00%

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