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Shareholders' Equity - Summary of Revaluation Reserve for Available-for-sale Investments (Detail) - shares
shares in Millions
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Disclosure of revaluation reserve [Line Items]      
Revaluation reserve for available-for-sale investments 4,348 1,910 3,427
Equity securities [member]      
Disclosure of revaluation reserve [Line Items]      
Revaluation reserve for available-for-sale investments 25 22 40
Debt securities [member]      
Disclosure of revaluation reserve [Line Items]      
Revaluation reserve for available-for-sale investments 4,348 1,911 3,401
Other securities [member]      
Disclosure of revaluation reserve [Line Items]      
Revaluation reserve for available-for-sale investments (26) (23) (14)