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Cash and Cash Equivalents - Annual Yield Rates of Bank Deposits, Commercial Paper, Negotiable Certificates of Deposit and Time Deposits (Detail)
Dec. 31, 2018
Dec. 31, 2017
Bank deposits [Member] | Bottom of range [Member]    
Disclosure of cash and cash equivalents [Line Items]    
Yield rate 0.00% 0.00%
Bank deposits [Member] | Top of Range [Member]    
Disclosure of cash and cash equivalents [Line Items]    
Yield rate 0.50% 0.70%
Commercial paper [Member] | Bottom of range [Member]    
Disclosure of cash and cash equivalents [Line Items]    
Yield rate 0.47% 0.32%
Commercial paper [Member] | Top of Range [Member]    
Disclosure of cash and cash equivalents [Line Items]    
Yield rate 0.57% 0.40%
Negotiable certificate of deposit [Member] | Bottom of range [Member]    
Disclosure of cash and cash equivalents [Line Items]    
Yield rate 0.55% 0.40%
Negotiable certificate of deposit [Member] | Top of Range [Member]    
Disclosure of cash and cash equivalents [Line Items]    
Yield rate 0.60% 0.50%
Time deposits [Member] | Bottom of range [Member]    
Disclosure of cash and cash equivalents [Line Items]    
Yield rate 0.09% 0.52%
Time deposits [Member] | Top of Range [Member]    
Disclosure of cash and cash equivalents [Line Items]    
Yield rate 4.40% 4.40%