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COMMON SHARES - Common Shares Authorized and Issued (Details) - $ / shares | Sep. 30, 2021 | Dec. 31, 2020 | Jun. 30, 2020 | Mar. 31, 2020
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Class of Stock [Line Items] |  |  |  |
Par value (in dollars per share) | $ 5 |  | $ 5 | $ 5
Authorized (in shares) | 380,000,000 | 380,000,000 |  |
Issued (in shares) | 357,818,402 | 357,818,402 |  |
CL&P |  |  |  |
Class of Stock [Line Items] |  |  |  |
Par value (in dollars per share) | $ 10 |  |  |
Authorized (in shares) | 24,500,000 | 24,500,000 |  |
Issued (in shares) | 6,035,205 | 6,035,205 |  |
NSTAR Electric |  |  |  |
Class of Stock [Line Items] |  |  |  |
Par value (in dollars per share) | $ 1 |  |  |
Authorized (in shares) | 100,000,000 | 100,000,000 |  |
Issued (in shares) | 200 | 200 |  |
PSNH |  |  |  |
Class of Stock [Line Items] |  |  |  |
Par value (in dollars per share) | $ 1 |  |  |
Authorized (in shares) | 100,000,000 | 100,000,000 |  |
Issued (in shares) | 301 | 301 |  |

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- Definition The maximum number of common shares permitted to be issued by an entity's charter and bylaws. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(29)) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
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- Definition Total number of common shares of an entity that have been sold or granted to shareholders (includes common shares that were issued, repurchased and remain in the treasury). These shares represent capital invested by the firm's shareholders and owners, and may be all or only a portion of the number of shares authorized. Shares issued include shares outstanding and shares held in the treasury. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(29)) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
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