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Pension and other post-retirement benefits - Weighted Average Assumptions Used to Determine Net Benefit Cost (Detail)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Pension benefits
Defined Benefit Plan Disclosure [Line Items]
Discount rate	5.35%	2.94%
Expected return on assets	6.38%	6.19%
Rate of compensation increase	3.99%	3.91%
OPEB
Defined Benefit Plan Disclosure [Line Items]
Discount rate	5.49%	3.00%
Expected return on assets	6.45%	6.48%
Health care cost trend rate
Before Age 65	6.00%	5.88%
Age 65 and after	6.00%	5.88%
Assumed ultimate medical inflation rate	4.75%	4.75%
Year in which ultimate rate is reached	2033	2031

X

- Definition

Defined Benefit Plan Health Care Cost Trend Rate Assumed For Next Fiscal Year Post Sixty Five

+ References

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- Definition

Defined Benefit Plan Health Care Cost Trend Rate Assumed For Next Fiscal Year Pre Sixty Five

+ References

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- Definition

Defined Benefit Plan, Ultimate Health Care Cost, Inflation Rate

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- Definition

Weighted average rate for present value of future retirement benefits cash flows, used to determine net periodic benefit cost of defined benefit plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (k)(1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

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X

- Definition

Weighted average rate of return on plan assets, reflecting average rate of earnings expected on existing plan assets and expected contributions, used to determine net periodic benefit cost of defined benefit plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 8
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-8

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (k)(3)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

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- Definition

Weighted average rate of compensation increase used to determine net periodic benefit cost of defined benefit plan. Plan includes, but is not limited to, pay-related defined benefit plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (k)(2)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

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- Definition

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

+ References

No definition available.

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- Definition

Year ultimate health care cost trend rate is expected to be reached, in YYYY format.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (l)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480506/715-20-50-1

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