Commitments, Guarantees and Contingencies (Details Textuals) (USD $)	3 Months Ended			3 Months Ended		3 Months Ended	1 Months Ended	3 Months Ended		3 Months Ended						3 Months Ended			3 Months Ended			3 Months Ended			3 Months Ended		3 Months Ended				3 Months Ended				3 Months Ended		16 Months Ended	0 Months Ended	3 Months Ended					0 Months Ended	3 Months Ended				3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012	Mar. 31, 2013 Clean Water Act	Apr. 30, 2009 Clean Water Act aspect_of_opinion	Mar. 31, 2013 Regulation of Waste Disposal options	Dec. 31, 2012 Nuclear Plant Matters	Mar. 31, 2013 Nuclear Plant Matters	Dec. 28, 2012 Nuclear Plant Matters decision	Mar. 31, 2013 Caa Compliance CoalFiredPlants ElectricGenerationUnits	Mar. 31, 2013 National Ambient Air Quality Standards T	Mar. 31, 2013 National Ambient Air Quality Standards CAIR phases	Mar. 31, 2013 National Ambient Air Quality Standards CSAPR phases	Mar. 31, 2012 Hazardous Air Pollutant Emissions	Mar. 31, 2013 Hazardous Air Pollutant Emissions	Mar. 31, 2013 Climate Change celsius	Apr. 13, 2012 Climate Change lb	Jan. 02, 2011 Climate Change T	Mar. 31, 2013 Climate Change Year 2020 Increase in funding	Mar. 31, 2013 Senior Secured Term Loan Senior Loans	Mar. 31, 2013 Regulated Distribution	Mar. 31, 2013 FES	Mar. 31, 2012 FES	Dec. 31, 2012 FES	Mar. 31, 2012 FES Hazardous Air Pollutant Emissions	Mar. 31, 2013 AE Supply	Mar. 31, 2013 AE Supply ICG Litigation	Mar. 31, 2013 Global Holding	Mar. 31, 2013 Global Holding Senior Secured Term Loan Senior Loans	Mar. 31, 2013 Global Holding Senior Secured Term Loan Senior Loans Signal Peak, Global Rail and Affiliates	Mar. 31, 2013 Signal Peak and Global Rail	Mar. 31, 2013 Signal Peak and Global Rail Senior Secured Term Loan Senior Loans	Mar. 31, 2013 FEV Senior Secured Term Loan Senior Loans Signal Peak Global Holding	Mar. 31, 2013 WMB Marketing Ventures, LLC Senior Secured Term Loan Senior Loans Signal Peak Global Holding	Mar. 31, 2013 FGCO	Dec. 31, 2012 FGCO	Feb. 27, 2007 FGCO Clean Water Act spills	Jan. 10, 2013 FGCO Clean Water Act Subsequent Event acre	Mar. 31, 2013 FGCO Caa Compliance Complaints	Mar. 31, 2013 FGCO Caa Compliance Claim One IndividualsInAComplaint Complaints	Mar. 31, 2013 FGCO Caa Compliance Claim Two plantiffs	Aug. 13, 2012 AE Supply and MP ICG Litigation	May 02, 2011 AE Supply and MP ICG Litigation	Feb. 13, 2012 WP	Mar. 31, 2013 WP	Mar. 31, 2013 Parental Guarantees	Mar. 31, 2013 Subsidiaries' Guarantees	Mar. 31, 2013 Other Guarantees	Mar. 31, 2013 State and Local Agencies Hazardous Air Pollutant Emissions	Mar. 31, 2013 Environmental Protection Agency Hazardous Air Pollutant Emissions	Mar. 31, 2013 Transportation Commitment Hazardous Air Pollutant Emissions	Apr. 13, 2012 Minimum Climate Change	Apr. 13, 2012 Maximum Climate Change	Dec. 31, 2013 Forecast Nuclear Plant Matters
Guarantor Obligations [Line Items]
Outstanding guarantees and other assurances aggregated	$ 4,000,000,000																																													$ 900,000,000	$ 2,400,000,000	$ 800,000,000
Company posted collateral related to net liability positions																					18,000,000	88,000,000
Potential collateral posted related to net liability positions																						109,000,000				6,000,000
Senior secured term loan facility, term																												3 years			2 years
New syndicated senior secured term loan facility																													350,000,000
Repayments of senior secured term loan facility	956,000,000	16,000,000																				543,000,000	0									350,000,000			107,000,000
Investment ownership percentage																														69.99%			33.33%	33.33%
Guarantor obligations, guarantee fee receivable, percentage, remainder of fiscal year																				4.00%
Guarantor obligations, guarantee fee receivable, percentage, next twelve months																				5.00%
Number of complaints filed against FGCO																																							3
Number of complaints seek enjoin plant																																							2	1
Number of individuals behalf of which complaint filed																																								21
Number of named plaintiffs as class representatives																																									8
Reduction in air emissions and compliance										81.00%																																										25.00%	40.00%
Number of electric generation facilities										10
Number of generation units										22
Number of phases under the EPA’s CAIR for reductions of Sulfur Dioxide and Mono-Nitrogen Oxides												2	2
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
Potential cost of compliance, MATS						234,000,000									925,000,000
Waste Disposal, Complaint Period						60 days
Pre-tax severance expense related to closures														7,000,000											4,000,000
Upper threshold limit for carbon dioxide emission (Tons per Year)																		75,000
Increase (decrease) in global temperature																2
Funds provided for Copenhagen Green Climate Fund																30,000,000,000			100,000,000,000
Commitment Period by Developed Countries to Provide Funds, Years																3 years
Commitment, Proposed Emissions Standard																	1,000
Aspects of opinion reversed					1
Annual percentage that fish impingement should be reduced to, per CWA				12.00%
Loss Contingency, Damages Awarded, Value																																						125,000
Loss Contingency, Damages Awarded, Area of Land in Damages																																						195
Petroleum spills																																					3
Maximum capital investment required to install technology to meet TDS and Sulfate limits				150,000,000
TMDL Limit Development Period				5 years
Executed Agreements, Public Comment Period																																						30 days
Claims resolution, civil penalties						800,000																																						86,000
Options proposed by EPA for additional regulation of coal combustion residuals						2
Accrual for Environmental Loss Contingencies						124,000,000
Environmental Liabilities Former Gas Facilities						81,000,000
Decommissioning Fund Investments	2,227,000,000		2,204,000,000					2,200,000,000														1,306,000,000		1,283,000,000											0	0
Parental guarantee associated with the funding of decommissioning costs								95,000,000																																														125,000,000
Parental Guarantee Associated With Funding Of Decommissioning Costs, Additions							11,000,000
Dismissal Motions Granted									2
Renewal length of operating license for Davis-Besse Nuclear Power Station								20 years
Final rule, determination period								24 months
Loss incurred in damages for replacement coal purchased																											80,000,000
Additional damages incurred for future shortfalls																											150,000,000
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
Potential MATS Extension Period																																																	1 year	1 year
Loss contingency, maximum																																																			60,000,000
Loss Contingency, Damages Awarded, Compensatory, Value																																													48,000,000
Loss Contingency, Damages Awarded, Punitive, Value																																													61,000,000
Gain contingency, damages denied																																										$ 90,000,000