Asset Retirement Obligations (Details Textuals) (USD $)	3 Months Ended	6 Months Ended	12 Months Ended
	Mar. 31, 2011	Jun. 30, 2011	Dec. 31, 2011 percent years	Dec. 31, 2010 years
Asset Retirement Obligations [Line Items]
Revision in estimated cash flows	$ 19,000,000	$ 20,000,000	$ (1,000,000)	$ 22,000,000
Reserve and Impairment of Retirement Obligation		6,000,000
Proposed Extension of Nuclear Plant 2 License				20
Decommissioning Expenses Current			1,400,000,000
Decommissioning Liability, Noncurrent			148,000,000	149,000,000
Inflation Rate Used to Determine Estimated Decommissioning Expenditures			6.00%
Nuclear Decommissioning Liabilities Funded Through Surcharge and Included In ARO Balance			1,400,000,000
Fermi 2 [Member]
Asset Retirement Obligations [Line Items]
Decommissioning Liability, Noncurrent			$ 10,000,000,000