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The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
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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.

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Regulatory and Rate Matters - Facebook Data Center Project (Details)	12 Months Ended
	Dec. 31, 2018 power_purchase_agreement Facility MW	Dec. 31, 2021 MW	Oct. 01, 2021 MW	Jul. 28, 2021 MW	Jun. 23, 2021 MW	Feb. 08, 2021 MW
Public Utilities, General Disclosures [Line Items]
Ownership percentage		50.00%
Facebook Data Center
Public Utilities, General Disclosures [Line Items]
Solar distributed generation (in mw)				190		190
PPA term	25 years
Number of megawatts in battery storage facilities (in megawatts)			100	100	100	100
Solar generation capacity expected to be operational (in megawatts)				50		50
Number of megawatts in battery storage facilities approved (in megawatts)			50	50
PNMR Development
Public Utilities, General Disclosures [Line Items]
Solar distributed generation (in mw)		130
Ownership percentage		50.00%
PNMR Development \| Facebook Data Center
Public Utilities, General Disclosures [Line Items]
Solar distributed generation (in mw)	50
Casa Mesa Wind, LLC \| Facebook Data Center
Public Utilities, General Disclosures [Line Items]
Solar distributed generation (in mw)	50
Avangrid Renewables, LLC \| Facebook Data Center
Public Utilities, General Disclosures [Line Items]
Solar distributed generation (in mw)	166
Route 66 Solar Energy Center, LLC \| Facebook Data Center
Public Utilities, General Disclosures [Line Items]
Solar distributed generation (in mw)	50
NMRD \| Facebook Data Center
Public Utilities, General Disclosures [Line Items]
Solar distributed generation (in mw)	100
Number of additional PPAs \| power_purchase_agreement	2
Number of solar facilities \| Facility	2