Asset Retirement Obligations (Details) - USD ($) $ in Millions		9 Months Ended		12 Months Ended
		Sep. 30, 2015		Dec. 31, 2014		Dec. 31, 2013
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
AROs at beginning of period	[1]	$ 1,714		$ 1,578
Obligations incurred during the period		307	[2]	40
Obligations settled during the period		(72)		(82)
Revisions in estimated cash flows		35	[2]	102	[3]
Accretion		69		81
Other		(1)		(5)
AROs at end of period	[1]	2,052		1,714
Aggregate fair value of trusts dedicated to funding decommissioning of nuclear plants		4,000		4,200
Other Current Liabilities
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
AROs reported in other current liabilities		228		81		$ 94
Virginia Electric and Power Company
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
AROs at beginning of period		855	[4]	689
Obligations incurred during the period		288	[2]	28
Obligations settled during the period		(22)		(1)
Revisions in estimated cash flows		32	[2]	108	[3]
Accretion		36		37
Other				(6)
AROs at end of period	[4]	1,189		855
Aggregate fair value of trusts dedicated to funding decommissioning of nuclear plants		1,900		1,900
Virginia Electric and Power Company | Other Current Liabilities
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
AROs reported in other current liabilities		$ 159		$ 7

[1] Includes $94 million, $81 million and $228 million reported in other current liabilities at December 31, 2013, December 31, 2014 and September 30, 2015, respectively.

[2] Primarily reflects future ash pond and landfill closure costs at certain utility generation facilities. See Note 16 for further information.

[3] Relates primarily to a shift of the delayed planned date on which the DOE is expected to begin accepting spent nuclear fuel.

[4] Includes $7 million and $159 million reported in other current liabilities at December 31, 2014 and September 30, 2015, respectively.