Commitments and Contingencies (Details) (USD $)	3 Months Ended	6 Months Ended	9 Months Ended			9 Months Ended
	Mar. 31, 2011 years	Jun. 30, 2011 employees years	Sep. 30, 2011 percent people years kWh Days weeks MCF banks customers ratio employees	Sep. 30, 2011 Electric Utility [Member] facility	Dec. 31, 2010 Electric Utility [Member]	Sep. 30, 2011 Gas Utility [Member] facility	Dec. 31, 2010 Gas Utility [Member]
Loss Contingencies [Line Items]
Environmental Capital Expenditures Through Prior Year			$ 1,500,000,000
Environmental Capital Expenditures in Current Year			200,000,000
Environmental Capital Expenditures In Future Years			2,000,000,000
Possible Additional Capital Exepnditures for EPA Regulations			80,000,000
Minimum Amount of Years to Incur Additional Capital Expenditures			4
Maximum Amount of Years to Incur Additional Capital Expenditures			6
Number of Former MGP Sites				3		15
Accrued for remediation related to the sites				8,000,000	9,000,000	41,000,000	36,000,000
Period Gas Utility Can Amortize MGP Costs			10
Possible Environmental Capital Expenditures to Comply with Requirements			1,500,000
Capital Expenditures Over the Next Few Years			13,000,000
Re-proposed Regulations Minimum Period of Compliance with Applicable Standards	3
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
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
Performance Bonds Outstanding			14,000,000
Number of Represented Employees			5,000
Years for Bargaining Unit Contract		3
Number of Represented Employees Who Ratified New Contract		400
Long-term Purchase Commitment, Amount			5,000,000,000
estimated future capital expenditures for current year			$ 1,700,000,000