Operating Segments Information - Major Customers Representing at Least 10 Percent of Net Revenue (Detail) $ in Millions, $ in Millions	12 Months Ended
Dec. 31, 2017 TWD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 TWD ($)	Dec. 31, 2015 TWD ($)
Disclosure of major customers [line items]
NET REVENUE	$ 977,447.2	$ 32,977.3	$ 947,938.3	$ 843,497.4
Customer A [member]
Disclosure of major customers [line items]
NET REVENUE	$ 214,228.8		$ 157,185.4	$ 134,117.2
Percentage of entity's revenue	22.00%	22.00%	17.00%	16.00%
Customer B [member]
Disclosure of major customers [line items]
NET REVENUE	$ 64,096.2		$ 107,463.2	$ 134,158.4
Percentage of entity's revenue	7.00%	7.00%	11.00%	16.00%

The income arising in the course of an entity's ordinary activities. Income is increases in economic benefits during the accounting period in the form of inflows or enhancements of assets or decreases of liabilities that result in an increase in equity, other than those relating to contributions from equity participants.

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+ Details