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Employee Benefit Plans (Effect of One Percentage Point Change on Benefit Plans) (Detail) - Other Postretirement Benefits $ in Millions | 12 Months Ended
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Dec. 31, 2017 USD ($)
Defined Benefit Plan Disclosure [Line Items] |
Effect of one percentage point increase on total of service and interest cost components | $ 24
Effect of one percentage point increase on other postretirement benefit obligation | 158
Effect of one percentage point decrease on total of service and interest cost components | (15)
Effect of one percentage point decrease on other postretirement benefit obligation | (132)
Dominion Energy Gas Holdings, LLC |
Defined Benefit Plan Disclosure [Line Items] |
Effect of one percentage point increase on total of service and interest cost components | 4
Effect of one percentage point increase on other postretirement benefit obligation | 31
Effect of one percentage point decrease on total of service and interest cost components | (3)
Effect of one percentage point decrease on other postretirement benefit obligation | $ (26)

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- Definition Amount of decrease in accumulated postretirement benefit obligation from one-percentage-point decrease in assumed health care cost trend rate. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (m) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Definition Amount of decrease in service and interest cost components of net periodic postretirement benefit cost from one-percentage-point decrease in assumed health care cost trend rate. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (m) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Definition Amount of increase in accumulated postretirement benefit obligation from one-percentage-point increase in assumed health care cost trend rate. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (m) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Definition Amount of increase in service and interest cost components of net periodic postretirement benefit cost from one-percentage-point increase in assumed health care cost trend rate. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (m) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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