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Bonds Payable - Summary of Bonds Payable (Detail)
$ in Millions, $ in Millions
Dec. 31, 2018
TWD ($)
Dec. 31, 2018
USD ($)
Dec. 31, 2017
TWD ($)
Bonds payable [line items]      
Less: Current portion $ (34,900.0)   $ (58,401.1)
Noncurrent bonds payable 56,900.0 $ 1,858.9 91,800.0
Overseas [member]      
Bonds payable [line items]      
Unsecured bonds   $ 1,150.0  
Cost [member]      
Bonds payable [line items]      
Unsecured bonds 91,800.0   150,207.8
Cost [member] | Taiwan [member]      
Bonds payable [line items]      
Unsecured bonds $ 91,800.0   116,100.0
Cost [member] | Overseas [member]      
Bonds payable [line items]      
Unsecured bonds     34,107.8
Discounts on bonds payable [member]      
Bonds payable [line items]      
Unsecured bonds     $ 6.7