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Pension and other post-employment benefits - Components of Net Benefit Costs for Pension Plans and OPEB Recorded as Part of Administrative Expenses (Detail) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2023 | Dec. 31, 2022
Non-service costs |  |
Non-service costs | $ 19,939 | $ 10,950
Pension benefits |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Service cost | 11,954 | 16,309
Non-service costs |  |
Interest cost | 33,687 | 24,787
Expected return on plan assets | (31,990) | (41,226)
Amortization of net actuarial losses (gains) | (852) | 3,452
Amortization of prior service credits | (1,491) | (1,584)
Amortization due to plan settlements | 0 | (15)
Impact of regulatory accounts | 16,258 | 22,952
Non-service costs | 15,612 | 8,366
Net benefit cost | 27,566 | 24,675
OPEB |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Service cost | 3,253 | 6,277
Non-service costs |  |
Interest cost | 11,510 | 9,146
Expected return on plan assets | (9,736) | (11,359)
Amortization of net actuarial losses (gains) | (3,559) | (56)
Amortization of prior service credits | (853) | 24
Amortization due to plan settlements | 0 | 0
Impact of regulatory accounts | 6,965 | 4,829
Non-service costs | 4,327 | 2,584
Net benefit cost | $ 7,580 | $ 8,861

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- Definition Amount of gain (loss) recognized in net periodic benefit (cost) credit of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 17 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480482/715-20-55-17 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 45 -Paragraph 3A -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480535/715-20-45-3A Reference 3: http://www.xbrl.org/2003/role/exampleRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 18 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480482/715-20-55-18 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (h)(4) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 6 -Subparagraph (a)(4) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-6 + Details
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- Definition Amount of prior service cost (credit) recognized in net periodic benefit cost (credit) of defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 17 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480482/715-20-55-17 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 45 -Paragraph 3A -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480535/715-20-45-3A Reference 3: http://www.xbrl.org/2003/role/exampleRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 18 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480482/715-20-55-18 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (h)(5) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-1 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 6 -Subparagraph (a)(5) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480506/715-20-50-6 + Details
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