XML 173 R155.htm IDEA: XBRL DOCUMENT v3.8.0.1
Additional Information of Expenses by Nature - Additional Information (Detail) - TWD ($)
$ in Millions
 12 Months Ended
Feb. 13, 2018
Feb. 14, 2017
Feb. 02, 2016
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Expense by nature [line items]            
Profit sharing bonus to employees, amount       $ 23,019.1 $ 22,418.3 $ 20,556.9
Director 1 [member]            
Expense by nature [line items]            
Approved profit sharing bonus in cash $ 368.9 $ 376.4 $ 356.2      
Employees [member]            
Expense by nature [line items]            
Approved profit sharing bonus in cash     $ 20,556.9      
Top of range [member] | Director 1 [member]            
Expense by nature [line items]            
Profit sharing bonus, percentage       0.30% 0.30% 0.30%
Bottom of range [member] | Employees [member]            
Expense by nature [line items]            
Profit sharing bonus, percentage       1.00% 1.00% 1.00%