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Deferred Credits and Other Noncurrent Liabilities - Summary of Changes to Provision for Asset Retirement Obligations (Detail) - PHP (₱)
₱ in Millions
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Subclassifications Of Assets Liabilities And Equities [Abstract]    
Provision for asset retirement obligations at beginning of the year ₱ 1,767 ₱ 1,656
Additional liability 205 154
Accretion expenses 61 82
Revaluation due to change in IBR 39  
Change in assumptions (22)  
Gain on settlement of asset retirement obligation (50)  
Settlement of obligations and others   (125)
Provision for asset retirement obligations at end of the year ₱ 2,000 ₱ 1,767