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Short-Term Debt and Credit Agreements (Commercial Paper, Bank Loans and Letters of Credit Outstanding) (Parenthetical) (Detail) - USD ($) | Dec. 31, 2020 | Dec. 31, 2019
--- | --- | ---
Line Of Credit Facility [Line Items] |  |  |  |
Weighted-average percentage interest rates |  | 0.29% |  | 2.10%
Facility Limit | [2] | $ 6,000,000,000 | [1] | $ 6,000,000,000
Virginia Electric and Power Company |  |  |  |
Line Of Credit Facility [Line Items] |  |  |  |
Weighted-average percentage interest rates |  | 0.30% |  | 2.10%
Facility Limit | [3] | $ 6,000,000,000 | [1] | $ 6,000,000,000
Letter of Credit |  |  |  |
Line Of Credit Facility [Line Items] |  |  |  |
Facility Limit |  | 2,000,000,000.0 |  |
Letter of Credit | Virginia Electric and Power Company |  |  |  |
Line Of Credit Facility [Line Items] |  |  |  |
Facility Limit |  | 2,000,000,000.0 |  |
Line of Credit | Virginia Electric and Power Company |  |  |  |
Line Of Credit Facility [Line Items] |  |  |  |
Facility Limit |  | $ 1,500,000,000 |  |
[1] | In October 2020, the joint revolving credit facility was amended to remove Dominion Energy Gas as a co-borrower.
[2] | This credit facility matures in March 2023 and can be used by the borrowers under the credit facility to support bank borrowings and the issuance of commercial paper, as well as to support up to a combined $2.0 billion of letters of credit.
[3] | The full amount of the facility is available to Virginia Power, less any amounts outstanding to co-borrowers Dominion Energy, Questar Gas and DESC. The sub-limit for Virginia Power is set within the facility limit but can be changed at the option of the borrowers under the credit facility multiple times per year. At December 31, 2020, the sub-limit for Virginia Power was $1.5 billion. If Virginia Power has liquidity needs in excess of its sub-limit, the sub-limit may be changed or such needs may be satisfied through short-term intercompany borrowings from Dominion Energy. This credit facility matures in March 2023 and can be used to support bank borrowings and the issuance of commercial paper, as well as to support up to $2.0 billion (or the sub-limit, whichever is less) of letters of credit.

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- Definition Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility. + 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 210.5-02.19(b),22(b)) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
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