Decommissioning Trust Funds (Details Textual) (USD $)	12 Months Ended
	Dec. 31, 2011 Y	Dec. 31, 2010	Dec. 31, 2009
Decommissioning Trust Funds (Textual) [Abstract]
Amortized cost of debt securities	$ 1,530,000,000	$ 1,475,000,000
Average coupon rate of debt securities	4.15%
Average duration of debt securities	5.40
Average maturity of debt securities	8.53
Proceeds from the dispositions of debt securities	1,360,000,000	2,606,000,000	2,571,000,000
Gains from dispositions of debt securities, gross	29,000,000	69,000,000	80,000,000
Losses from dispositions of debt securities, gross	11,000,000	9,000,000	30,000,000
Adjustments to retained earnings, before tax			11,300,000
Adjustments to retained earnings, net of tax			6,400,000
Other than temporary impairment losses	(140,000)	(1,378,000)	(86,069,000)
Deferred taxes on unrealized gains/(losses) recorded in OCI for non-regulated decommissioning trusts	$ 149,000,000	$ 130,000,000