Summary of significant accounting policies - Nuclear decommissioning funds (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Nuclear decommissioning funds
Additional contribution to external trust funds	$ 8,632	$ 4,619
Additional amount collected for nuclear decommissioning	$ 8,333	$ 10,000
Percentage of decommissioning fund classified as equity	51.00%	71.00%
Percentage of decommissioning funds classified as fixed income securities	34.00%	29.00%
Percentage of decommissioning funds classified as cash	15.00%
External and Internal Trust Funds:
Purchases	$ 1,149,281	$ 535,027	$ 204,500
Fair Value	721,624	641,239
External Trust Funds
External and Internal Trust Funds:
Cost		444,090	422,013
Purchases	1,149,283	535,027
Net Proceeds	(1,049,165)	(512,950)
Unrealized Gain(Loss)	177,416	197,149
Fair Value	721,624	641,239
Net realized gains or losses, interest income and dividends, contributions and fees	100,118	22,078
Internal Funds
External and Internal Trust Funds:
Cost		135,698	122,154
Purchases	139,657	59,630
Net Proceeds	(112,841)	(46,086)
Unrealized Gain(Loss)	38,286	38,192
Fair Value	200,800	173,890
Net realized gains or losses, interest income and dividends, contributions and fees	26,817	13,542
Equity \| External Trust Funds
External and Internal Trust Funds:
Cost		249,063	228,936
Purchases	169,927	29,307
Net Proceeds	(75,461)	(9,180)
Unrealized Gain(Loss)	186,129	201,900
Fair Value	529,658	450,963
Equity \| Internal Funds
External and Internal Trust Funds:
Cost		86,378	79,122
Purchases	0	0
Net Proceeds	3,257	7,256
Unrealized Gain(Loss)	40,466	39,134
Fair Value	130,101	125,512
Debt \| External Trust Funds
External and Internal Trust Funds:
Cost		195,756	192,986
Purchases	788,109	485,705
Net Proceeds	(781,509)	(482,935)
Unrealized Gain(Loss)	(8,713)	(4,751)
Fair Value	193,643	191,005
Debt \| Internal Funds
External and Internal Trust Funds:
Cost		49,320	43,032
Purchases	139,657	59,630
Net Proceeds	(116,098)	(53,342)
Unrealized Gain(Loss)	(2,180)	(942)
Fair Value	70,699	48,378
Other \| External Trust Funds
External and Internal Trust Funds:
Cost		(729)	$ 91
Purchases	191,247	20,015
Net Proceeds	(192,195)	(20,835)
Unrealized Gain(Loss)	0	0
Fair Value	$ (1,677)	$ (729)

Represents the amount of additional contribution to external nuclear decommissioning trust funds.

No definition available.

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- Definition

Amount collected from members for nuclear decommissioning.

+ References

No definition available.

+ Details

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- Definition

The fair value of investments held in a trust fund to pay for the costs of decontaminating and decommissioning facilities, including net realized gains (losses), interest income and dividends, and contributions and fees.

+ References

No definition available.

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- Definition

Includes the cash inflow from the sale of assets held in a decommissioning trust fund, net realized gains or losses, interest income and dividends, contributions and fees.

+ References

No definition available.

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The total amount of net realized gains or losses, interest income and dividends, contributions and fees, during the reporting period.

+ References

No definition available.

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- Definition

Nuclear Decommissioning Trust Fund [Line Items]

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No definition available.

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- Definition

Percentage Of Decommissioning Funds Classified As Cash Pending Reallocation

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No definition available.

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- Definition

Represents the percentage of decommissioning funds classified as equity.

+ References

No definition available.

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- Definition

Represents the percentage of decommissioning funds classified as fixed income securities.

+ References

No definition available.

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- Definition

Decommission fund to pay for the costs of decontaminating and decommissioning of facilities through collection of revenues derived from utility assessments and government appropriations. Decommission fund investment for the process whereby a power station, at the end of its economic life, is taken permanently out of service and its site made available for other purposes. In the case of a nuclear station this comprises three different states of clearance. Immediately after the final closure, radioactive material such as nuclear fuel and operational waste is removed and the buildings surrounding the reactor shield are dismantled and finally the reactor itself is dismantled.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(12))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1

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- Definition

The cash outflow for the purchase of investments that will be held in a decommissioning trust fund.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 230
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 13
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482740/230-10-45-13

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- Definition

Amount of unrealized gain (loss) on investment.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 45
-Paragraph 28
-Subparagraph (b)
-SubTopic 10
-Topic 230
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482740/230-10-45-28

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