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Subsidiaries - Less Than Wholly Owned Subsidiaries of the Company That Have Material Noncontrolling Interests (Detail) $ in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2019 TWD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 TWD ($)	Dec. 31, 2017 TWD ($)	Dec. 31, 2019 USD ($)	Jan. 01, 2019 TWD ($)
Disclosure of subsidiaries [Line Items]
Profit Allocated to Noncontrolling Interests	$ 974	$ 32	$ 1,024	$ 1,172
Accumulated Noncontrolling Interests	$ 10,115		$ 9,857		$ 338	$ 9,837
Senao International Co., Ltd. (SENAO) [Member]
Disclosure of subsidiaries [Line Items]
Place of Incorporation	Taiwan	Taiwan
Principal Place of Business	Taiwan	Taiwan
Proportion of Ownership Interests Held by Noncontrolling Interests	72.00%	72.00%	72.00%
Proportion of Voting Rights Held by Noncontrolling Interests	72.00%	72.00%	72.00%
Profit Allocated to Noncontrolling Interests	$ 291		$ 326	592
Accumulated Noncontrolling Interests	$ 4,146		$ 4,108
Chunghwa Precision Test Tech. Co., Ltd. (CHPT) [Member]
Disclosure of subsidiaries [Line Items]
Place of Incorporation	Taiwan	Taiwan
Principal Place of Business	Taiwan	Taiwan
Proportion of Ownership Interests Held by Noncontrolling Interests	66.00%	66.00%	66.00%
Proportion of Voting Rights Held by Noncontrolling Interests	66.00%	66.00%	66.00%
Profit Allocated to Noncontrolling Interests	$ 414		$ 477	$ 431
Accumulated Noncontrolling Interests	4,217		4,022
Individually immaterial subsidiaries with noncontrolling interests [Member]
Disclosure of subsidiaries [Line Items]
Accumulated Noncontrolling Interests	$ 1,752		$ 1,727