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Goodwill and Intangible Assets (Goodwill) (Detail) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016
Goodwill [Roll Forward] |  |  |
Goodwill, Beginning Balance | [1] | $ 6,399 | $ 3,294
Dominion Questar Combination |  | 6 |
Goodwill, Ending Balance | [1] | 6,405 | 6,399
Dominion Energy Gas Holdings, LLC |  |  |
Goodwill [Roll Forward] |  |  |
Goodwill, Beginning Balance | [1] | 542 | 542
No events affecting goodwill |  | 0 | 0
Goodwill, Ending Balance | [1] | 542 | 542
Dominion Questar Corporation |  |  |
Goodwill [Roll Forward] |  |  |
Dominion Questar Combination |  |  | 3,105
Operating Segments | Power Generation |  |  |
Goodwill [Roll Forward] |  |  |
Goodwill, Beginning Balance | [1] | 1,422 | 1,422
Goodwill, Ending Balance | [1] | 1,422 | 1,422
Operating Segments | Power Generation | Dominion Energy Gas Holdings, LLC |  |  |
Goodwill [Roll Forward] |  |  |
No events affecting goodwill |  | 0 | 0
Operating Segments | Gas Infrastructure |  |  |
Goodwill [Roll Forward] |  |  |
Goodwill, Beginning Balance | [1] | 4,051 | 946
Dominion Questar Combination |  | 6 |
Goodwill, Ending Balance | [1] | 4,057 | 4,051
Operating Segments | Gas Infrastructure | Dominion Energy Gas Holdings, LLC |  |  |
Goodwill [Roll Forward] |  |  |
Goodwill, Beginning Balance | [1] | 542 | 542
No events affecting goodwill |  | 0 | 0
Goodwill, Ending Balance | [1] | 542 | 542
Operating Segments | Power Delivery |  |  |
Goodwill [Roll Forward] |  |  |
Goodwill, Beginning Balance | [1] | 926 | 926
Goodwill, Ending Balance | [1] | 926 | 926
Operating Segments | Power Delivery | Dominion Energy Gas Holdings, LLC |  |  |
Goodwill [Roll Forward] |  |  |
No events affecting goodwill |  | 0 | 0
Operating Segments | Corporate and Other | Dominion Energy Gas Holdings, LLC |  |  |
Goodwill [Roll Forward] |  |  |
No events affecting goodwill | [2] | $ 0 | 0
Operating Segments | Dominion Questar Corporation | Gas Infrastructure |  |  |
Goodwill [Roll Forward] |  |  |
Dominion Questar Combination | [3] |  | $ 3,105
[1] | Goodwill amounts do not contain any accumulated impairment losses.
[2] | Goodwill recorded at the Corporate and Other segment is allocated to the primary operating segments for goodwill impairment testing purposes.
[3] | See Note 3.

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