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Cash and Cash Equivalents - Annual Yield Rates of Bank Deposits, Commercial Paper, Negotiable Certificate of Deposit and Time Deposits (Detail) | Dec. 31, 2017 | Dec. 31, 2016
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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 | 0.70% | 0.42%
Commercial paper [Member] | Bottom of range [Member] |  |
Disclosure of cash and cash equivalents [Line Items] |  |
Yield rate | 0.32% | 0.32%
Commercial paper [Member] | Top of range [Member] |  |
Disclosure of cash and cash equivalents [Line Items] |  |
Yield rate | 0.40% | 0.42%
Negotiable certificate of deposit [Member] | Bottom of range [Member] |  |
Disclosure of cash and cash equivalents [Line Items] |  |
Yield rate | 0.40% | 0.35%
Negotiable certificate of deposit [Member] | Top of range [Member] |  |
Disclosure of cash and cash equivalents [Line Items] |  |
Yield rate | 0.50% | 0.50%
Time deposits [Member] | Bottom of range [Member] |  |
Disclosure of cash and cash equivalents [Line Items] |  |
Yield rate | 0.52% | 0.40%
Time deposits [Member] | Top of range [Member] |  |
Disclosure of cash and cash equivalents [Line Items] |  |
Yield rate | 4.40% | 3.30%

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- Details
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- Details
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- Details
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- Details
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