Equity (Narrative) (Detail)			1 Months Ended											2 Months Ended	3 Months Ended	12 Months Ended
	Aug. 15, 2016 shares	[1]	Jan. 31, 2019 USD ($) shares	Dec. 31, 2018 USD ($) shares	Jun. 30, 2018 USD ($) shares	May 31, 2018	Apr. 30, 2018 shares	Feb. 28, 2018 USD ($) Agreement	Jan. 31, 2018 USD ($) Performance_Factor shares	Jul. 31, 2017 USD ($) shares	Jun. 30, 2017 USD ($) Agreement	Jul. 31, 2016 shares	Apr. 30, 2016 USD ($) shares	Apr. 30, 2018 shares	Dec. 31, 2018 USD ($) shares	Dec. 31, 2019 shares	Dec. 31, 2018 USD ($) Performance_Factor shares	Dec. 31, 2017 USD ($) shares	Dec. 31, 2016 USD ($) shares	Sep. 30, 2015 USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Issuance of common stock																	$ 2,461,000,000	$ 1,302,000,000	$ 2,152,000,000
Common stock, shares outstanding | shares				681,000,000											681,000,000		681,000,000	645,000,000
Issuance of common stock (in shares)																	$ 2,461,000,000	$ 1,302,000,000	2,152,000,000
Net proceeds from issuance of Dominion Midstream common units																	$ 4,000,000	18,000,000	482,000,000
Net proceeds from issuance of Dominion Midstream convertible preferred units																			490,000,000
Conversion basis				1											1		1
Subordinated unit conversion						1
Number of shares received | shares					26,700,000
Increase (decrease) Non-controlling interest					$ 375,000,000
Compensation cost related to stock-based compensation																	$ 48,000,000	45,000,000	33,000,000
Tax benefit from stock awards and stock options exercised																	$ 12,000,000	16,000,000	11,000,000
Vesting period																	3 years
Subsequent Event
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock issued in acquisition | shares			22,500,000
Shares of common stock issued in acquisition, value			$ 1,600,000,000
Cash Based Performance Grant | Officer
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Cash-based performance grants minimum percentage																	0.00%
Cash-based performance grants maximum percentage																	200.00%
February 2016 Cash Based Performance Grant | Officer
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of performance metrics achieved | Performance_Factor									2
Expected award under grant									$ 12,000,000
February 2017 Cash Based Performance Grant [Member] | Officer
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of performance metrics achieved | Performance_Factor																	2
February 2017 Cash Based Performance Grant [Member] | Officer | Two-year grant
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Targeted amount of the grant				$ 13,000,000											$ 13,000,000		$ 13,000,000
Liability accrued for award				13,000,000											13,000,000		13,000,000
February 2017 Cash Based Performance Grant [Member] | Officer | Three-year grant
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Targeted amount of the grant				14,000,000											14,000,000		14,000,000
Liability accrued for award				10,000,000											10,000,000		$ 10,000,000
February 2018 Cash Based Performance Grant [Member] | Officer
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of performance metrics achieved | Performance_Factor																	2
February 2018 Cash Based Performance Grant [Member] | Officer | Three-year grant
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Targeted amount of the grant				16,000,000											16,000,000		$ 16,000,000
Liability accrued for award				$ 5,000,000											$ 5,000,000		$ 5,000,000
Dominion Direct Employee Stock Awards Employee Savings Plans Director Stock Compensation Plans and Contingent Convertible Senior Notes
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares for future agreement | shares				76,000,000											76,000,000		76,000,000
Stock Based Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares were available for future grants | shares				22,000,000											22,000,000		22,000,000
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost related to nonvested awards				$ 49,000,000											$ 49,000,000		$ 49,000,000
Fair value of restricted stock awards that vested																	$ 23,000,000	$ 21,000,000	$ 21,000,000
Virginia Electric and Power Company
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Issuance of common stock (in shares | shares																	0	0	0
Common stock, shares outstanding | shares				274,723											274,723		274,723	274,723
Repurchase of common stock, shares | shares																	0	0
Virginia Electric and Power Company | Scenario, Forecast
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Repurchase of common stock, shares | shares																0
Dominion Midstream Partners, LP | Limited Partner
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Net proceeds from issuance of Dominion Midstream common units																		$ 18,000,000	$ 482,000,000
Dominion Midstream Partners, LP | Limited Partner | Convertible Preferred Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Net proceeds from issuance of Dominion Midstream convertible preferred units																			$ 490,000,000
Dominion Midstream Partners, LP | Dominion Midstream Limited Partner Common Unit Purchase Program | Limited Partner
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Authorized purchase amount																				$ 50,000,000
Stock repurchase program expiration date																	Sep. 30, 2016
Number of common units purchased | shares																			658,000
Value of common units purchased																			$ 17,000,000
Maximum | Stock Based Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum term of stock based awards																	8 years
Weighted Average | Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected weighted-average period recognized for the unrecognized compensation cost																	2 years 1 month 6 days
Noncontrolling Interests
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Increase (decrease) Non-controlling interest					$ (375,000,000)
Goldman Sachs & Co. and Credit Suisse LLC.
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Issuance of common stock				$ 1,400,000,000
Issuance of common stock (in shares | shares				22,100,000
Number of shares for future agreement | shares							20,000,000							20,000,000
Capital Unit, Class A
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Issuance of common stock										$ 1,000,000,000
Issuance of common stock (in shares | shares	28,000,000									12,500,000
Capital Unit, Class A | Remarketable Subordinated Notes
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Issuance of common stock																	$ 1,100,000,000
Issuance of common stock (in shares | shares										12,500,000		8,500,000	8,500,000
Underwritten Public Offering
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Issuance of common stock													$ 756,000,000
Issuance of common stock (in shares | shares													10,200,000
Various Programs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Issuance of common stock																	$ 2,500,000,000
Issuance of common stock (in shares | shares																	36,000,000
Common stock, shares outstanding | shares				681,000,000											681,000,000		681,000,000
Employee Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Cash proceeds received from issuance of shares through Dominion Direct and employee savings plans																	$ 315,000,000
Number of shares issued through Dominion Direct and employee savings plans | shares																	4,500,000
Shelf Registration for Sale of Common Stock through At-the-market Program
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Issuance of common stock									$ 495,000,000						$ 197,000,000
Issuance of common stock (in shares | shares									6,600,000						2,700,000
Number of sales agency agreements | Agreement								6			3
Issuance of common stock (in shares)											$ 0
Fees and commissions paid									$ 5,000,000						$ 2,000,000
Remaining ability to issue stock under the sales agency agreements				$ 801,000,000											$ 801,000,000		$ 801,000,000
Shelf Registration for Sale of Common Stock through At-the-market Program | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Sale of stock authorized amount								$ 1,000,000,000			$ 500,000,000
Underwriting Agreement | Goldman Sachs & Co. and Credit Suisse LLC.
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Option exercised | shares							2,100,000
Underwriting Agreement | Goldman Sachs & Co. and Credit Suisse LLC. | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares granted for service | shares														3,000,000

[1] The maturity dates of the $700 million Series A-1 RSNs and $700 million Series A-2 RSNs are August 15, 2021 and August 15, 2024, respectively.