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Pensions and Other Post-employment Benefit Obligations - Summary of Actuarial Assumptions (Parenthetical) (Detail)	Dec. 31, 2017
2018 [member] | Pre 65 [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Medical trend rate	7.00%
2018 [member] | Post 65 [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Medical trend rate	6.00%
2026 [member] | Pre 65 [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Medical trend rate	4.50%
2026 [member] | Post 65 [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Medical trend rate	4.50%

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- Definition

Medical cost trend rate used as significant actuarial assumption to determine the present value of a defined benefit obligation. [Refer: Defined benefit obligation, at present value; Actuarial assumptions [member]]

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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-IssueDate 2017-01-01
-Paragraph 144
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-URIDate 2017-03-09

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- Definition

Line items represent concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes of the table.

+ References

No definition available.

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