Organization and Basis of Presentation (Details Textuals) customer in Millions						1 Months Ended		3 Months Ended			6 Months Ended	12 Months Ended
	Apr. 02, 2018 USD ($)	Dec. 13, 2017 USD ($)	Oct. 20, 2017	Aug. 30, 2017 USD ($) Natural_gas_plant	Jul. 22, 2016 MW	Aug. 31, 2017 USD ($) Natural_gas_plant MW	Jan. 31, 2017 USD ($) MW	Dec. 31, 2017 USD ($) transmission_center MW	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($) customer transmission_center company mi MW	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Jan. 31, 2018 USD ($)	Mar. 06, 2017 USD ($) MW	Jan. 18, 2017
Regulatory Assets [Line Items]
Aggregate amount of capacity (in MWs) | MW													16,000
Length of transmission lines | mi													24,500
Number of regional transmission centers | transmission_center								2					2
Impairment of assets															$ 42,000,000
Regulatory assets that do not earn a current return								$ 7,000,000	$ 153,000,000				$ 7,000,000	$ 153,000,000
Capitalized financing costs													35,000,000	37,000,000	49,000,000
Interest costs capitalized													44,000,000	66,000,000	68,000,000
Property, plant and equipment								$ 28,879,000,000	29,387,000,000				28,879,000,000	29,387,000,000
Other than temporary impairments													13,000,000	21,000,000	102,000,000
Impairments of long-lived assets													2,406,000,000	10,665,000,000	42,000,000
Net cash used for financing activities													(702,000,000)	(34,000,000)	(292,000,000)
Net cash provided by (used in) operating activities													$ 3,808,000,000	3,383,000,000	3,460,000,000
Regulated Distribution
Regulatory Assets [Line Items]
Number of existing utility operating companies | company													10
Number of customers served by utility operating companies | customer													6
Plant generation capacity (in MW's) | MW								3,790					3,790
Impairment of assets															8,000,000
Property, plant and equipment, net								$ 2,100,000,000					$ 2,100,000,000
Property, plant and equipment								$ 18,916,000,000	18,282,000,000				$ 18,916,000,000	18,282,000,000
Competitive Energy Services
Regulatory Assets [Line Items]
Plant generation capacity (in MW's) | MW								12,303					12,303
Impairment of assets									9,218,000,000						34,000,000
Impairment of assets													$ 193,000,000
Property, plant and equipment								$ 972,000,000	2,866,000,000				$ 972,000,000	2,866,000,000
Bath County, Virginia
Regulatory Assets [Line Items]
Plant generation capacity (in MW's) | MW								3,003					3,003
MP
Regulatory Assets [Line Items]
Ownership interest (percent)													41.00%
Virginia Electric and Power Company | Bath County, Virginia
Regulatory Assets [Line Items]
Proportionate ownership share (percent)								60.00%					60.00%
FES
Regulatory Assets [Line Items]
Impairment of assets								$ 2,045,000,000							33,000,000
Interest costs capitalized													$ 26,000,000	34,000,000	35,000,000
Property, plant and equipment								694,000,000	1,555,000,000				694,000,000	1,555,000,000
Other than temporary impairments													13,000,000	19,000,000	90,000,000
Impairments of long-lived assets													2,031,000,000	8,622,000,000	33,000,000
Net cash used for financing activities													(166,000,000)	56,000,000	(273,000,000)
Net cash provided by (used in) operating activities													$ 727,000,000	786,000,000	1,152,000,000
FES | Competitive Energy Services
Regulatory Assets [Line Items]
Impairment of assets								2,000,000,000	8,082,000,000
Impairment of assets								$ 2,000,000,000
AGC | Bath County, Virginia
Regulatory Assets [Line Items]
Plant generation capacity (in MW's) | MW								1,200					1,200
Proportionate ownership share (percent)								40.00%					40.00%
Property, plant and equipment								$ 531,000,000					$ 531,000,000
AGC | Bath County, Virginia | Competitive Energy Services
Regulatory Assets [Line Items]
Property, plant and equipment								$ 365,000,000					$ 365,000,000
Signal Peak | Global Holding | FEV
Regulatory Assets [Line Items]
Ownership interest (percent)								33.33%					33.33%
Impairments of long-lived assets														362,000,000
Bay Shore Unit 1
Regulatory Assets [Line Items]
Plant capacity (in MW's) | MW					136
Sammis Power Plant Units 1-4
Regulatory Assets [Line Items]
Plant capacity (in MW's) | MW					720
Pleasants Power Station
Regulatory Assets [Line Items]
Plant generation capacity (in MW's) | MW																	1,300
Assets purchase agreement consideration to be received																	$ 195,000,000
Impairment of assets								$ 120,000,000
Forecast | FES | Competitive Energy Services
Regulatory Assets [Line Items]
Debt that needs to be refinanced												$ 515,000,000
Principal payment	$ 100,000,000
Purchase Agreement with Subsidiary of LS Power
Regulatory Assets [Line Items]
Plant generation capacity (in MW's) | MW						1,615		756					756
Cash purchase price						$ 825,000,000	$ 825,000,000
Plant capacity (in MW's) | MW							1,615
Purchase Agreement with Subsidiary of LS Power | AE Supply
Regulatory Assets [Line Items]
Number of gas generating plants | Natural_gas_plant				4		4
Discharge of note indenture				$ 305,000,000
Make-whole premiums													$ 95,000,000
Ownership interest (percent)													59.00%
Purchase Agreement with Subsidiary of LS Power | AE Supply | Bath County, Virginia
Regulatory Assets [Line Items]
Proportionate ownership share (percent)																		23.75%
Purchase Agreement with Subsidiary of LS Power | AGC
Regulatory Assets [Line Items]
Plant ownership percentage			59.00%	59.00%		59.00%
Make-whole premiums													$ 95,000,000
Purchase Agreement with Subsidiary of LS Power | Natural Gas Generating Plants
Regulatory Assets [Line Items]
Cash purchase price		$ 388,000,000
Purchase Agreement with Subsidiary of LS Power | Forecast | Bath County Hydroelectric Power Station and Buchanan Generating Facility
Regulatory Assets [Line Items]
Cash purchase price											$ 375,000,000
Subsequent Event
Regulatory Assets [Line Items]
Maximum amount borrowed under revolving credit facility																$ 5,000,000,000
Subsequent Event | FES
Regulatory Assets [Line Items]
Maximum amount borrowed under revolving credit facility																500,000,000
Line of Credit | Revolving Credit Facility
Regulatory Assets [Line Items]
Maximum amount borrowed under revolving credit facility								$ 5,000,000,000	500,000,000				5,000,000,000	500,000,000
Line of Credit | Revolving Credit Facility | FES
Regulatory Assets [Line Items]
Maximum amount borrowed under revolving credit facility									500,000,000					500,000,000
Line of Credit | Revolving Credit Facility | Subsequent Event
Regulatory Assets [Line Items]
Maximum amount borrowed under revolving credit facility																5,000,000,000
Line of Credit | Revolving Credit Facility | Subsequent Event | FES
Regulatory Assets [Line Items]
Maximum amount borrowed under revolving credit facility																$ 500,000,000
Utilization of Accelerated Useful Life
Regulatory Assets [Line Items]
Out-of period adjustment										$ 21,000,000				19,000,000
Accounting Standards Update 2016-09
Regulatory Assets [Line Items]
Net cash used for financing activities														12,000,000	13,000,000
Net cash provided by (used in) operating activities														(12,000,000)	(13,000,000)
Accounting Standards Update 2017-07 | Pro Forma
Regulatory Assets [Line Items]
Reclassification of non-service costs													62,000,000
Retained Earnings (Accumulated Deficit)
Regulatory Assets [Line Items]
Share-based compensation accounting change (Note 1)								(6,000,000)					(6,000,000)
Retained Earnings (Accumulated Deficit) | Accounting Standards Update 2016-09
Regulatory Assets [Line Items]
Share-based compensation accounting change (Note 1)									$ 6,000,000					6,000,000
Retained Earnings (Accumulated Deficit) | Accounting Standards Update 2016-01
Regulatory Assets [Line Items]
Share-based compensation accounting change (Note 1)								115,000,000					115,000,000
Retained Earnings (Accumulated Deficit) | Accounting Standards Update 2016-01 | FES
Regulatory Assets [Line Items]
Share-based compensation accounting change (Note 1)								$ 115,000,000					$ 115,000,000
Deferred Purchased Power and Fuel Costs
Regulatory Assets [Line Items]
Prior period reclassification adjustment														(30,000,000)	(105,000,000)
Amortization of Regulatory Assets, Net
Regulatory Assets [Line Items]
Prior period reclassification adjustment														$ 30,000,000	$ 105,000,000
PCRB | Purchase Agreement with Subsidiary of LS Power | AE Supply
Regulatory Assets [Line Items]
Discharge of note indenture				$ 142,000,000
Senior Notes | Purchase Agreement with Subsidiary of LS Power | AGC
Regulatory Assets [Line Items]
Discharge of note indenture				$ 100,000,000