Accumulated Other Comprehensive Income (Schedule of Changes in AOCI by Component Net of Tax) (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2017	Mar. 31, 2016
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	[1]	$ 14,605
Total other comprehensive income		64	$ 11
Ending balance		14,917
Dominion Gas Holdings, LLC
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	[2]	3,536
Total other comprehensive income		2	(8)
Ending balance		3,640
Total
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance		(799)	(474)
Other comprehensive income before reclassifications: gains		102	68
Amounts reclassified from AOCI: (gains) losses	[3]	(38)	(57)
Total other comprehensive income		64	11
Ending balance		(735)	(463)
Total | Dominion Gas Holdings, LLC
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance		(123)	(99)
Other comprehensive income before reclassifications: gains		(9)	(6)
Amounts reclassified from AOCI: (gains) losses	[3]	11	(2)
Total other comprehensive income		2	(8)
Ending balance		(121)	(107)
Deferred Gains and Losses on Derivatives-Hedging Activities
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance		(280)	(176)
Other comprehensive income before reclassifications: gains		43	53
Amounts reclassified from AOCI: (gains) losses	[3]	(23)	(63)
Total other comprehensive income		20	(10)
Ending balance		(260)	(186)
Deferred Gains and Losses on Derivatives-Hedging Activities | Dominion Gas Holdings, LLC
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance		(24)	(17)
Other comprehensive income before reclassifications: gains		(9)	(6)
Amounts reclassified from AOCI: (gains) losses	[3]	11	(2)
Total other comprehensive income		2	(8)
Ending balance		(22)	(25)
Unrealized Gains and Losses on Investment Securities
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance		569	504
Other comprehensive income before reclassifications: gains		58	15
Amounts reclassified from AOCI: (gains) losses	[3]	(28)	(2)
Total other comprehensive income		30	13
Ending balance		599	517
Unrecognized Pension and Other Postretirement Benefit Costs
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance		(1,082)	(797)
Other comprehensive income before reclassifications: gains		0	0
Amounts reclassified from AOCI: (gains) losses	[3]	13	8
Total other comprehensive income		13	8
Ending balance		(1,069)	(789)
Unrecognized Pension and Other Postretirement Benefit Costs | Dominion Gas Holdings, LLC
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance		(99)	(82)
Other comprehensive income before reclassifications: gains		0	0
Amounts reclassified from AOCI: (gains) losses	[3]	0	0
Total other comprehensive income		0	0
Ending balance		(99)	(82)
Other Comprehensive Income (Loss) From Equity Method Investee
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance		(6)	(5)
Other comprehensive income before reclassifications: gains		1	0
Amounts reclassified from AOCI: (gains) losses	[3]	0	0
Total other comprehensive income		1	0
Ending balance		$ (5)	$ (5)

[1] Dominion’s Consolidated Balance Sheet at December 31, 2016 has been derived from the audited Consolidated Balance Sheet at that date.

[2] Dominion Gas’ Consolidated Balance Sheet at December 31, 2016 has been derived from the audited Consolidated Balance Sheet at that date.

[3] See table below for details about these reclassifications.