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Post-Employment Benefits - Summary of Sensitivity of Defined Benefit Obligation (Parenthetical) (Detail)	Dec. 31, 2018
Medical care cost [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Percentage increase in assumptions	8.16%
BD and CV Plans [member] | Actuarial assumption of interest rates [member] | Actuarial liabilities [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Percentage increase in assumptions	0.50%
Percentage decrease in assumptions	0.50%
BD and CV Plans [member] | Actuarial assumption of mortality rates [member] | Actuarial liabilities [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Percentage increase in assumptions	5.00%
Percentage decrease in assumptions	5.00%
Other post employment benefits [member] | Actuarial assumption of interest rates [member] | Actuarial liabilities [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Percentage increase in assumptions	0.50%
Percentage decrease in assumptions	0.50%
Other post employment benefits [member] | Actuarial assumption of mortality rates [member] | Actuarial liabilities [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Percentage increase in assumptions	5.00%
Percentage decrease in assumptions	5.00%
Other post employment benefits [member] | Medical care cost [member] | Actuarial liabilities [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Percentage increase in assumptions	1.00%
Percentage decrease in assumptions	1.00%
Stockholders Equity [Member] | BD and CV Plans [member] | Actuarial assumption of interest rates [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Percentage increase in assumptions	0.50%
Percentage decrease in assumptions	0.50%
Stockholders Equity [Member] | BD and CV Plans [member] | Actuarial assumption of mortality rates [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Percentage increase in assumptions	5.00%
Percentage decrease in assumptions	5.00%
Stockholders Equity [Member] | Other post employment benefits [member] | Actuarial assumption of interest rates [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Percentage increase in assumptions	0.50%
Percentage decrease in assumptions	0.50%
Stockholders Equity [Member] | Other post employment benefits [member] | Actuarial assumption of mortality rates [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Percentage increase in assumptions	5.00%
Percentage decrease in assumptions	5.00%
Stockholders Equity [Member] | Other post employment benefits [member] | Medical care cost [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Percentage increase in assumptions	1.00%
Percentage decrease in assumptions	1.00%

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The reasonably possible percentage of the decrease in the actuarial assumption used to determine the present value of defined benefit obligation. [Refer: Actuarial assumptions [member]]

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The reasonably possible percentage of the increase in the actuarial assumption used to determine the present value of defined benefit obligation. [Refer: Actuarial assumptions [member]]

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