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Available-for-Sale Securities (Details) (USD $)
In Millions
3 Months Ended9 Months Ended
Sep. 30, 2011
Sep. 30, 2010
Sep. 30, 2011
Sep. 30, 2010
Dec. 31, 2010
Available-for-sale securities balance sheet details [Abstract]     
Amortized cost$ 475 $ 475 $ 624
Gross unrealized gains145 145 182
Gross unrealized losses2 2 0
Fair value618 618 806
Available-for-sale securities proceeds from and realized gains and losses [Abstract]     
Proceeds from sales of NDT securities34[1]15[1]13483 
Other proceeds from sales001630 
Gross realized gains3[2]2[2]26[2]11[2] 
Gross realized losses4[2]1[2]15[2]4[2] 
Short Term Investments - Municipal Debt Securities [Member]
     
Available-for-sale securities balance sheet details [Abstract]     
Amortized cost0 0 163
Gross unrealized gains0 0 0
Gross unrealized losses0 0 0
Fair value0 0 163
Short Term Investments [Abstract]     
Principal amount of tax-exempt revenue bonds held as short-term investment163 163  
Proceeds received from the remarketing of certain Kentucky tax-exempt revenue bonds  163  
Nuclear Decommissioning Trust Funds [Member]
     
Available-for-sale securities balance sheet details [Abstract]     
Amortized cost450 450 436
Gross unrealized gains145 145 182
Gross unrealized losses1 1 0
Fair value594 594 618
Nuclear Decommissioning Trust Funds [Member] | Cash and Cash Equivalents [Member]
     
Available-for-sale securities balance sheet details [Abstract]     
Amortized cost13 13 10
Gross unrealized gains0 0 0
Gross unrealized losses0 0 0
Fair value13 13 10
Nuclear Decommissioning Trust Funds [Member] | Equity Securities [Member] | US Large Cap [Member]
     
Available-for-sale securities balance sheet details [Abstract]     
Amortized cost170 170 180
Gross unrealized gains90 90 123
Gross unrealized losses0 0 0
Fair value260 260 303
Nuclear Decommissioning Trust Funds [Member] | Equity Securities [Member] | US Mid Small Cap [Member]
     
Available-for-sale securities balance sheet details [Abstract]     
Amortized cost67 67 67
Gross unrealized gains37 37 52
Gross unrealized losses0 0 0
Fair value104 104 119
Nuclear Decommissioning Trust Funds [Member] | Debt Securities [Member] | US Treasury [Member]
     
Available-for-sale securities balance sheet details [Abstract]     
Amortized cost72 72 71
Gross unrealized gains10 10 4
Gross unrealized losses0 0 0
Fair value82 82 75
Nuclear Decommissioning Trust Funds [Member] | Debt Securities [Member] | US Government Sponsored Agency [Member]
     
Available-for-sale securities balance sheet details [Abstract]     
Amortized cost10 10 6
Gross unrealized gains1 1 1
Gross unrealized losses0 0 0
Fair value11 11 7
Nuclear Decommissioning Trust Funds [Member] | Debt Securities [Member] | Municipal Debt Securities [Member]
     
Available-for-sale securities balance sheet details [Abstract]     
Amortized cost79 79 69
Gross unrealized gains4 4 0
Gross unrealized losses1 1 0
Fair value82 82 69
Nuclear Decommissioning Trust Funds [Member] | Debt Securities [Member] | Other [Member]
     
Available-for-sale securities balance sheet details [Abstract]     
Amortized cost3 3 1
Gross unrealized gains0 0 0
Gross unrealized losses0 0 0
Fair value3 3 1
Nuclear Decommissioning Trust Funds [Member] | Receivables Payables Net [Member]
     
Available-for-sale securities balance sheet details [Abstract]     
Amortized cost2 2 1
Gross unrealized gains0 0 0
Gross unrealized losses0 0 0
Fair value2 2 1
Auction Rate Securities [Member]
     
Available-for-sale securities balance sheet details [Abstract]     
Amortized cost25 25 25
Gross unrealized gains0 0 0
Gross unrealized losses1 1 0
Fair value24 24 25
Debt Securities [Member]
     
Available-for-sale securities scheduled maturity dates of debt securities [Abstract]     
Amortized cost - maturity less than 1 year10 10  
Amortized cost - maturity between 1 and 5 years70 70  
Amortized cost - maturity between 5 and 10 years64 64  
Amortized cost - maturity in excess of 10 years79 79  
Amortized cost total223 223  
Fair value - maturity less than 1 year10 10  
Fair value - maturity between 1 and 5 years73 73  
Fair value - maturity between 5 and 10 years70 70  
Fair value - maturity in excess of 10 years86 86  
Fair value total239 239  
Investment Grade Corporate [Member]
     
Available-for-sale securities balance sheet details [Abstract]     
Amortized cost34 34 31
Gross unrealized gains3 3 2
Gross unrealized losses0 0 0
Fair value$ 37 $ 37 $ 33
[1]These proceeds are used to pay income taxes and fees related to managing the trust. Remaining proceeds are reinvested in the trust.
[2]Excludes the impact of other-than-temporary impairment charges recognized in the Statements of Income.