Commitments, Guarantees and Contingencies (Details Textuals) (USD $)	12 Months Ended			3 Months Ended	0 Months Ended					3 Months Ended	0 Months Ended
	Dec. 31, 2014 Nuclear_Power_Plant	Dec. 31, 2013	Dec. 31, 2012	Jun. 30, 2013	Oct. 10, 2013 IndividualsInAComplaint	Oct. 03, 2013	Mar. 28, 2013	Feb. 09, 2015 IndividualsInAComplaint	Oct. 23, 2014	Dec. 31, 2013	Jul. 01, 2014	Apr. 19, 2013 option	Dec. 31, 2011 mi	Nov. 12, 2014	Apr. 30, 2014	Apr. 13, 2012 lb	Aug. 13, 2012	May 02, 2011	Feb. 13, 2015
Guarantor Obligations [Line Items]
Liability assessed with respect to single nuclear incident	$ 13,600,000,000
Plants licensed to operate	104
Portion of insurance coverage of private insurer included in single nuclear incident	375,000,000
Portion of insurance coverage by industry retrospective rating plan	13,200,000,000
Losses in excess of private insurance contributed for each nuclear unit license	127,000,000
Losses in excess of private insurance contributed for each nuclear unit license per unit	19,000,000
Nuclear incidence liability per incident of parent and subsidiary companys based on their present nuclear ownership and leasehold interests	509,000,000
Nuclear incident liability not more than in any one year per incident of parent and subsidiary companies based on their present nuclear ownership and leasehold interests	76,000,000
Aggregate indemnity	1,960,000,000
Maximum aggregate assessments for incidents at any covered nuclear facility	14,000,000
Coverage of decontamination costs	2,750,000,000
Retrospective assessments liabilities	74,000,000
Insurance coverage for replacement power costs	1,060,000,000
Environmental plan, submission period	30 days
Outstanding guarantees and other assurances aggregated	4,000,000,000
Repayments of senior secured term loan facility	1,759,000,000	3,600,000,000	940,000,000
Number of treatment options												8
Number of preferred treatment options												4
Renewal cycle of waste water discharge permit	5 years
Proposed sulfate impairment designation, length													68
Nuclear plant decommissioning trusts	2,341,000,000	2,201,000,000								2,201,000,000
ICG Litigation
Guarantor Obligations [Line Items]
Gain contingency, damages denied				15,500,000
Year 2020
Guarantor Obligations [Line Items]
Reduction in power plants carbon pollution, (percent)				17.00%
Clean Water Act
Guarantor Obligations [Line Items]
Annual percentage that fish impingement should be reduced to, per CWA	12.00%
TMDL limit development period	5 years
Regulation of Waste Disposal
Guarantor Obligations [Line Items]
Number of individuals behalf of which complaint filed					61
Civil penalties	800,000
Bond closure and post closure period						45 years
Period of time to implement plan							12 years
Accrual for environmental loss contingencies	125,000,000
Environmental liabilities former gas facilities	85,000,000
Regulation of Waste Disposal | Subsequent Event
Guarantor Obligations [Line Items]
Number of individuals behalf of which complaint filed								26
Nuclear Plant Matters
Guarantor Obligations [Line Items]
Nuclear plant decommissioning trusts	2,300,000,000
Parental guarantee associated with the funding of decommissioning costs	155,000,000
Additions to parental guarantee associated with funding of decommissioning costs	23,000,000
Renewal length of operating license	20 years
Caa Compliance
Guarantor Obligations [Line Items]
Loss in period	133,000,000
National Ambient Air Quality Standards
Guarantor Obligations [Line Items]
Capping of SO2 emissions (In Tons)	2,500,000
Capping of NOx emissions (In Tons)	1,300,000
Capping of SO2 Emissions Under CSAPR	2,400,000
Capping of NOx emissions under CSAPR	1,200,000
National Ambient Air Quality Standards | CAIR
Guarantor Obligations [Line Items]
Number of phases under the EPA’s CAIR for reductions of Sulfur Dioxide and Mono-Nitrogen Oxides	2
National Ambient Air Quality Standards | CSAPR
Guarantor Obligations [Line Items]
Period of delay in implementation of new regulation									3 years
Number of phases under the EPA’s CAIR for reductions of Sulfur Dioxide and Mono-Nitrogen Oxides	2
Hazardous Air Pollutant Emissions
Guarantor Obligations [Line Items]
Potential cost of compliance, MATS	370,000,000
Climate Change
Guarantor Obligations [Line Items]
Reduction in air emissions and compliance																25.00%
Reduction in GHG emissions between 2005 and 2012 (percent)															10.00%
Energy from renewable sources (percent)														20.00%
Proposed emissions standard, other natural gas fired units																1,100
Proposed emissions standard, fossil fuel fired units																1,100
Proposed emissions standard, large natural gas fired units																1,000
Senior Secured Term Loan | Senior Loans
Guarantor Obligations [Line Items]
Guarantor obligations, guarantee fee receivable, percentage, remainder of fiscal year	4.00%
Guarantor obligations, guarantee fee receivable, percentage, next twelve months	5.00%
Competitive Energy Services | Caa Compliance
Guarantor Obligations [Line Items]
Loss in period	56,000,000
Competitive Energy Services | Hazardous Air Pollutant Emissions
Guarantor Obligations [Line Items]
Potential cost of compliance, MATS	178,000,000
Regulated Distribution
Guarantor Obligations [Line Items]
Company posted collateral related to net liability positions	1,000,000
Regulated Distribution | Caa Compliance
Guarantor Obligations [Line Items]
Loss in period	77,000,000
Regulated Distribution | Hazardous Air Pollutant Emissions
Guarantor Obligations [Line Items]
Potential cost of compliance, MATS	192,000,000
FES
Guarantor Obligations [Line Items]
Company posted collateral related to net liability positions	175,000,000
Potential collateral posted related to net liability positions	24,000,000
Repayments of senior secured term loan facility	816,000,000	1,202,000,000	429,000,000
Nuclear plant decommissioning trusts	1,365,000,000	1,276,000,000								1,276,000,000
Global Holding
Guarantor Obligations [Line Items]
Senior secured term loan facility, term										3 years
Global Holding | Senior Secured Term Loan | Senior Loans
Guarantor Obligations [Line Items]
New syndicated senior secured term loan facility	350,000,000
Global Holding | Senior Secured Term Loan | Senior Loans | Signal Peak, Global Rail and Affiliates
Guarantor Obligations [Line Items]
Investment ownership percentage	69.99%
Signal Peak and Global Rail
Guarantor Obligations [Line Items]
Senior secured term loan facility, term										2 years
Signal Peak and Global Rail | Senior Secured Term Loan | Senior Loans
Guarantor Obligations [Line Items]
Repayments of senior secured term loan facility	350,000,000
FEV | Senior Secured Term Loan | Senior Loans | Signal Peak | Global Holding
Guarantor Obligations [Line Items]
Investment ownership percentage	33.33%
WMB Marketing Ventures, LLC | Senior Secured Term Loan | Senior Loans | Signal Peak | Global Holding
Guarantor Obligations [Line Items]
Investment ownership percentage	33.33%
FGCO
Guarantor Obligations [Line Items]
Repayments of senior secured term loan facility	269,000,000	364,000,000	288,000,000
Nuclear plant decommissioning trusts	0	0								0
FGCO | Caa Compliance
Guarantor Obligations [Line Items]
Number of complaints filed against FGCO	3
Number of complaints seek enjoin plant	2
FGCO | Caa Compliance | Claim One
Guarantor Obligations [Line Items]
Number of complaints seek enjoin plant	1
Number of individuals behalf of which complaint filed	21
FGCO | Caa Compliance | Claim Two
Guarantor Obligations [Line Items]
Number of named plaintiffs as class representatives	8
AE Supply and MP | ICG Litigation
Guarantor Obligations [Line Items]
Verdict in favor																		104,000,000
Amount for which verdict entered for future damages																		90,000,000
Amount for replacement coal and interest																		14,000,000
Gain contingency, unrecorded amount																	14,000,000
Value of damages denied																	90,000,000
AE Supply and MP | ICG Litigation | Subsequent Event
Guarantor Obligations [Line Items]
Amount for which verdict entered for future damages																			11,300,000
NGC
Guarantor Obligations [Line Items]
Nuclear incidence liability per incident of parent and subsidiary companys based on their present nuclear ownership and leasehold interests	501,000,000
Nuclear incident liability not more than in any one year per incident of parent and subsidiary companies based on their present nuclear ownership and leasehold interests	75,000,000
Aggregate indemnity	1,930,000,000
Maximum aggregate assessments for incidents at any covered nuclear facility	13,000,000
Retrospective assessments liabilities	72,000,000
Parental Guarantees
Guarantor Obligations [Line Items]
Outstanding guarantees and other assurances aggregated	712,000,000
Subsidiaries' Guarantees
Guarantor Obligations [Line Items]
Outstanding guarantees and other assurances aggregated	2,338,000,000
Other Guarantees
Guarantor Obligations [Line Items]
Outstanding guarantees and other assurances aggregated	649,000,000
Minimum | Clean Water Act
Guarantor Obligations [Line Items]
Maximum capital investment required to install technology to meet TDS and Sulfate limits	150,000,000
Minimum | Climate Change
Guarantor Obligations [Line Items]
Reduction in emissions (percent)														26.00%
Minimum | State and Local Agencies | Caa Compliance
Guarantor Obligations [Line Items]
Potential MATS extension period										1 year
Maximum | Clean Water Act
Guarantor Obligations [Line Items]
Maximum capital investment required to install technology to meet TDS and Sulfate limits	300,000,000
Maximum | Climate Change
Guarantor Obligations [Line Items]
Reduction in emissions (percent)														28.00%
Maximum | State and Local Agencies | Caa Compliance
Guarantor Obligations [Line Items]
Potential MATS extension period										2 years
Transportation Commitment | Caa Compliance
Guarantor Obligations [Line Items]
Potential cost of compliance, MATS	70,000,000
Settlement agreement, consideration											$ 67,000,000
Mass remaining under contract	6,000,000
Number of agreements	1