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Income Taxes (Unrecognized Tax Benefits) (Detail) - USD ($) $ in Millions | 1 Months Ended | 12 Months Ended
--- | --- | ---
Jun. 30, 2017 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward] |  |  |  |  |
Balance at January 1 |  | $ 44 |  | $ 38 | $ 64
Acquired unrecognized tax benefits |  | 129 | [1] | 0 | 0
Increases-prior period positions |  | 0 |  | 10 | 1
Decreases-prior period positions |  | 0 |  | 0 | (9)
Increases-current period positions |  | 9 |  | 10 | 5
Settlements with tax authorities |  | (7) |  | (6) | (23)
Expiration of statutes of limitations |  | 0 |  | (8) | 0
Balance at December 31 |  | 175 |  | 44 | 38
Virginia Electric and Power Company |  |  |  |  |
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward] |  |  |  |  |
Balance at January 1 |  | 2 |  | 4 | 13
Acquired unrecognized tax benefits |  | 0 |  | 0 | 0
Increases-prior period positions |  | 0 |  | 0 | 0
Decreases-prior period positions |  | 0 |  | 0 | (1)
Increases-current period positions |  | 0 |  | 0 | 0
Settlements with tax authorities | $ (8) | (2) |  | (1) | (8)
Expiration of statutes of limitations |  | 0 |  | (1) | 0
Balance at December 31 |  | 0 |  | 2 | 4
Dominion Energy Gas Holdings, LLC |  |  |  |  |
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward] |  |  |  |  |
Balance at January 1 |  | 2 |  | 2 | 9
Acquired unrecognized tax benefits |  | 0 |  | 0 | 0
Increases-prior period positions |  | 0 |  | 0 | 0
Decreases-prior period positions |  | 0 |  | 0 | 0
Increases-current period positions |  | 0 |  | 0 | 0
Settlements with tax authorities |  | 0 |  | 0 | (7)
Expiration of statutes of limitations |  | 0 |  | 0 | 0
Balance at December 31 |  | $ 2 |  | $ 2 | $ 2
[1] | Acquired unrecognized tax benefits reflect $106 million plus increases in prior period positions of $76 million and decreases in prior period positions of $53 million that were recorded through purchase accounting.

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- Definition Amount of unrecognized tax benefits. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 45 -Paragraph 10B -URI http://asc.fasb.org/extlink&oid=116821951&loc=SL37586934-109318 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15A -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=84230637&loc=SL6600010-109319 + Details
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