Asset Retirement Obligations (Details Textuals) (USD $)	3 Months Ended	6 Months Ended	12 Months Ended
	Mar. 31, 2011	Jun. 30, 2011	Dec. 31, 2012	Dec. 31, 2011
Asset Retirement Obligations [Line Items]
Liability Recorded for Non Estimatable Values of Assets Related to ARO			$ 0
Revision in estimated cash flows	19,000,000	20,000,000	10,000,000	22,000,000
Reserve and Impairment of Retirement Obligation		6,000,000
Proposed Extension of Nuclear Plant 2 License			20 years
Decommissioning Expenses Current			1,500,000,000
Decommissioning Liability, Noncurrent			159,000,000	148,000,000
Inflation Rate Used to Determine Estimated Decommissioning Expenditures			6.00%
Nuclear Decommissioning Liabilities Funded Through Surcharge and Included In ARO Balance			1,500,000,000
Liabilities Balance upon Completion of Decommissioning			0
Fermi 2 [Member]
Asset Retirement Obligations [Line Items]
Decommissioning Liability, Noncurrent			$ 10,000,000,000