Decommissioning Trust Funds (Details 1) (USD $)	3 Months Ended	9 Months Ended	12 Months Ended
Sep. 30, 2011 Year MMBtu	Sep. 30, 2010	Sep. 30, 2011 MW GeneratingUnit Year MMBtu	Sep. 30, 2010	Dec. 31, 2010
Fair value of debt securities by contractual maturities
Less than 1 year	$ 49,000,000		$ 49,000,000		$ 37,000,000
1 year - 5 years	553,000,000		553,000,000		557,000,000
5 years - 10 years	603,000,000		603,000,000		512,000,000
10 years - 15 years	183,000,000		183,000,000		163,000,000
15 years - 20 years	47,000,000		47,000,000		47,000,000
20 years+	201,000,000		201,000,000		204,000,000
Total	1,636,000,000		1,636,000,000		1,520,000,000
Decommissioning Trust Funds (Textuals) [Abstract]
Amortized cost of debt securities	1,504,000,000		1,504,000,000		1,475,000,000
Average coupon rate of debt securities	4.15%		4.15%
Average duration of debt securities	5.46		5.46
Average maturity of debt securities	8.65		8.65
Proceeds from the dispositions of debt securities	417,000,000	487,000,000	1,053,000,000	1,974,000,000
Gains from dispositions of debt securities, gross	12,000,000	10,000,000	21,000,000	34,000,000
Losses from dispositions of debt securities, gross	3,000,000	2,000,000	9,000,000	6,000,000
Recognition of other than temporary impairment charges to other income	0	0	0	0
Deferred taxes on unrealized gains/(losses) recorded in OCI for non-regulated decommissioning trusts			$ 106,000,000		$ 130,000,000

Available For Sale Securities Debt Maturities After Fifteen to twenty Years Fair Value.

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