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Notes and Accounts Receivable, Net - Summary of Notes and Accounts Receivable, Net (Detail)
$ in Millions, $ in Millions
Dec. 31, 2017
TWD ($)
Dec. 31, 2017
USD ($)
Dec. 31, 2016
TWD ($)
Disclosure of information about of trade accounts and notes receivables [Line Items]      
Notes and accounts receivable $ 121,133.2 $ 4,086.8 $ 128,335.3
Cost [member]      
Disclosure of information about of trade accounts and notes receivables [Line Items]      
Notes and accounts receivable 121,605.0   128,815.4
Allowance for doubtful receivables [member]      
Disclosure of information about of trade accounts and notes receivables [Line Items]      
Notes and accounts receivable $ (471.8)   $ (480.1)