Fair Value (Details Textuals) (USD $)	3 Months Ended		9 Months Ended												9 Months Ended	12 Months Ended			3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013 Fair Value, Measurements, Recurring [Member]	Dec. 31, 2012 Fair Value, Measurements, Recurring [Member]	Sep. 30, 2013 Fair Value, Inputs, Level 2 [Member] Fair Value, Measurements, Recurring [Member]	Dec. 31, 2012 Fair Value, Inputs, Level 2 [Member] Fair Value, Measurements, Recurring [Member]	Sep. 30, 2013 Restricted Assets [Member] Fair Value, Inputs, Level 2 [Member] Fair Value, Measurements, Recurring [Member]	Dec. 31, 2012 Restricted Assets [Member] Fair Value, Inputs, Level 2 [Member] Fair Value, Measurements, Recurring [Member]	Sep. 30, 2013 Other Investments [Member] Fair Value, Measurements, Recurring [Member] Equity [Member]	Dec. 31, 2012 Other Investments [Member] Fair Value, Measurements, Recurring [Member] Equity [Member]	Sep. 30, 2013 Other Investments [Member] Fair Value, Inputs, Level 2 [Member] Fair Value, Measurements, Recurring [Member]	Dec. 31, 2012 Other Investments [Member] Fair Value, Inputs, Level 2 [Member] Fair Value, Measurements, Recurring [Member]	Sep. 30, 2013 Nuclear Decommissioning Trust Fund [Member]	Dec. 31, 2012 Nuclear Decommissioning Trust Fund [Member]	Sep. 30, 2013 Fermi 2 [Member]	Dec. 31, 2012 Fermi 2 [Member]	Sep. 30, 2013 Fermi 1 [Member]	Sep. 30, 2012 Fermi 1 [Member]	Sep. 30, 2013 Fermi 1 [Member]	Sep. 30, 2012 Fermi 1 [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure					$ 68,000,000	$ 123,000,000	$ 68,000,000	$ 123,000,000	$ 51,000,000	$ 109,000,000			$ 17,000,000	$ 14,000,000	$ 12,000,000	$ 7,000,000
Available-for-sale Securities, Fair Value Disclosure											6,000,000	5,000,000
Other investments					124,000,000	110,000,000	48,000,000	44,000,000			124,000,000	110,000,000
Average Maturity of Debt Securities															7 years	6 years
Unrealized losses recognized as regulatory assets																	38,000,000	44,000,000
Fermi I Corresponding Regulatory Asset Treatment																			0		0
Unrealized losses recognized in earnings																			0	0	0	0
Unrealized on Available for Sale Securities	0	0	0	0
Trading Securities, Change in Unrealized Holding Gain (Loss)			$ 14,000,000	$ 11,000,000