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Goodwill - Additional Information (Detail) - USD ($)	3 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Goodwill [Line Items]
Additions due to acquisitions			$ 42,000,000
Impairment loss of goodwill	$ 0	$ 0
Accumulated impairment losses, net		102,000,000	102,000,000
Microcontrollers and Digital ICs Group (MDG) [Member]
Goodwill [Line Items]
Additions due to acquisitions			42,000,000
Accumulated impairment losses, net		96,000,000	96,000,000
Microcontrollers and Digital ICs Group (MDG) [Member] | NFC and RFID Reader Business [Member]
Goodwill [Line Items]
Additions due to acquisitions		42,000,000
Others [Member]
Goodwill [Line Items]
Accumulated impairment losses, net		$ 6,000,000	$ 6,000,000

X

- Definition

Amount of increase in asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized resulting from a business combination.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

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- Definition

Amount of accumulated impairment loss for an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a,h)
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- Definition

Amount of loss from the write-down of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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-Topic 350
-SubTopic 20
-Section 50
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-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585

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