Commitments and Contingencies (Details Textuals) (USD $)	3 Months Ended	12 Months Ended
	Dec. 31, 2011 employees	Dec. 31, 2011 weeks kWh years people employees	Dec. 31, 2010
Loss Contingencies [Line Items]
Environmental Capital Expenditures Through Current Year		$ 1,700,000,000
Environmental Capital Expenditures in Current Year		255,000,000
Environmental Capital Expenditures In Future Years	1,900,000,000
Possible Additional Capital Exepnditures for EPA Regulations		80,000,000	55,000,000
Minimum Amount of Years to Incur Additional Capital Expenditures		4
Maximum Amount of Years to Incur Additional Capital Expenditures		6
Period Gas Utility Can Amortize MGP Costs		10
Possible Environmental Capital Expenditures to Comply with Requirements		1,000,000
Capital Expenditures Over the Next Few Years		13,000,000
Number of Defendant Oil Power and Coal Companies In Domestic District Court on Basis of Which Company Named		24
Number of People In Country Claiming Business Activities Contributing to Global Warming Higher Temperatures and Storm Activity		400
Costs associated with relocating village and unspecified attorney's fees and expenses	400,000,000	400,000,000
Waiting Period of Policy		12
Insurance Coverage for Extra ExpenseWhen to Necessitate Power Plant when Unavailable		490,000,000
Period of Coverage of Policy for Extra Expenses		3
Primary Coverage		500,000,000
Coverage for Stabilization Decontamination Debris Removal Repair and Replacement of Property and Decommissioning		2,250,000,000
Combined Coverage Limit for Total Property Damage		2,750,000,000
NEIL Policies Against Terroism Loss		3,200,000,000
Amount per Event Loss Associated with Nuclear Power Plants		29,000,000
Maintenance of Public Liability Insurance for Nuclear Power Plants		375,000,000
Aggregate Limit of Liabilities Arises From Terroist Act Outside Scope of Trials Subject to One Industry		300,000,000
Deferred Premium Charged Leviied Against Each Licensed Nuclear Facility		117,500,000
Limit Deferred Premium Charges Per Year		17,500,000
Company Obligated to Pay DOE Fee of Fermi 2 Electricity Generated and Sold		1
Guarantee Obligations Maximum Exposure One	10,000,000	10,000,000
Performance Bonds Outstanding	23,000,000	23,000,000
Number of Represented Employees	5,000	5,000
Long-term Purchase Commitment, Amount		5,300,000,000
estimated future capital expenditures for current year	1,900,000,000	1,900,000,000
Electric Utility [Member]
Loss Contingencies [Line Items]
Number of Former MGP Sites		3
Accrued for remediation related to the sites	8,000,000	8,000,000	9,000,000
Gas Utility [Member]
Loss Contingencies [Line Items]
Number of Former MGP Sites		15
Accrued for remediation related to the sites	36,000,000	36,000,000	36,000,000
Synthetic Fuel [Member]
Loss Contingencies [Line Items]
Days Obligations will Survive After Expiration of All Applicable Statutes of Limiations	90	90
Guarantor Obligations, Maximum Exposure, Undiscounted	1,200,000,000	1,200,000,000
Emissions [Member]
Loss Contingencies [Line Items]
Days Obligations will Survive After Expiration of All Applicable Statutes of Limiations	90	90
Guarantor Obligations, Maximum Exposure, Undiscounted	$ 0	$ 0