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SONGS NDT 1 (Details) (USD $) In Millions, unless otherwise specified
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3 Months Ended |
12 Months Ended |
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Mar. 31, 2015
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Mar. 31, 2014
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Dec. 31, 2014
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| Schedule of Available-for-sale Securities [Line Items] |
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| Cost |
$ 685us-gaap_AvailableForSaleSecuritiesAmortizedCost |
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$ 675us-gaap_AvailableForSaleSecuritiesAmortizedCost |
| Gross Unrealized Gains |
477us-gaap_AvailableForSaleSecuritiesGrossUnrealizedGains |
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466us-gaap_AvailableForSaleSecuritiesGrossUnrealizedGains |
| Gross Unrealized Loss |
(12)us-gaap_AvailableForSaleSecuritiesGrossUnrealizedLoss |
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(10)us-gaap_AvailableForSaleSecuritiesGrossUnrealizedLoss |
| Estimated fair value |
1,150us-gaap_AvailableForSaleSecurities |
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1,131us-gaap_AvailableForSaleSecurities |
| Proceeds from sales |
94us-gaap_AvailableForSaleSecuritiesGrossRealizedGainsLossesSaleProceeds |
[1] |
195us-gaap_AvailableForSaleSecuritiesGrossRealizedGainsLossesSaleProceeds |
[1] |
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| Gross realized gains |
2us-gaap_AvailableForSaleSecuritiesGrossRealizedGains |
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4us-gaap_AvailableForSaleSecuritiesGrossRealizedGains |
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| Gross realized losses |
(4)us-gaap_AvailableForSaleSecuritiesGrossRealizedLosses |
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(4)us-gaap_AvailableForSaleSecuritiesGrossRealizedLosses |
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| Total Debt Securities |
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| Schedule of Available-for-sale Securities [Line Items] |
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| Cost |
448us-gaap_AvailableForSaleSecuritiesAmortizedCost / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_DebtSecuritiesMember |
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430us-gaap_AvailableForSaleSecuritiesAmortizedCost / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_DebtSecuritiesMember |
| Gross Unrealized Gains |
25us-gaap_AvailableForSaleSecuritiesGrossUnrealizedGains / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_DebtSecuritiesMember |
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21us-gaap_AvailableForSaleSecuritiesGrossUnrealizedGains / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_DebtSecuritiesMember |
| Gross Unrealized Loss |
(8)us-gaap_AvailableForSaleSecuritiesGrossUnrealizedLoss / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_DebtSecuritiesMember |
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(6)us-gaap_AvailableForSaleSecuritiesGrossUnrealizedLoss / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_DebtSecuritiesMember |
| Estimated fair value |
465us-gaap_AvailableForSaleSecurities / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_DebtSecuritiesMember |
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445us-gaap_AvailableForSaleSecurities / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_DebtSecuritiesMember |
| Debt Securities Issued By The U.S. Treasury And Other U.S. Government Corporations And Agencies |
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| Schedule of Available-for-sale Securities [Line Items] |
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| Cost |
103us-gaap_AvailableForSaleSecuritiesAmortizedCost / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USTreasuryAndGovernmentMember |
[2] |
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103us-gaap_AvailableForSaleSecuritiesAmortizedCost / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USTreasuryAndGovernmentMember |
| Gross Unrealized Gains |
8us-gaap_AvailableForSaleSecuritiesGrossUnrealizedGains / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USTreasuryAndGovernmentMember |
[2] |
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6us-gaap_AvailableForSaleSecuritiesGrossUnrealizedGains / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USTreasuryAndGovernmentMember |
| Gross Unrealized Loss |
0us-gaap_AvailableForSaleSecuritiesGrossUnrealizedLoss / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USTreasuryAndGovernmentMember |
[2] |
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0us-gaap_AvailableForSaleSecuritiesGrossUnrealizedLoss / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USTreasuryAndGovernmentMember |
| Estimated fair value |
111us-gaap_AvailableForSaleSecurities / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USTreasuryAndGovernmentMember |
[2] |
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109us-gaap_AvailableForSaleSecurities / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USTreasuryAndGovernmentMember |
| Municipal Bonds |
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| Schedule of Available-for-sale Securities [Line Items] |
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| Cost |
134us-gaap_AvailableForSaleSecuritiesAmortizedCost / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember |
[3] |
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121us-gaap_AvailableForSaleSecuritiesAmortizedCost / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember |
| Gross Unrealized Gains |
8us-gaap_AvailableForSaleSecuritiesGrossUnrealizedGains / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember |
[3] |
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8us-gaap_AvailableForSaleSecuritiesGrossUnrealizedGains / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember |
| Gross Unrealized Loss |
0us-gaap_AvailableForSaleSecuritiesGrossUnrealizedLoss / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember |
[3] |
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0us-gaap_AvailableForSaleSecuritiesGrossUnrealizedLoss / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember |
| Estimated fair value |
142us-gaap_AvailableForSaleSecurities / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember |
[3] |
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129us-gaap_AvailableForSaleSecurities / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember |
| Other Debt Securities |
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| Schedule of Available-for-sale Securities [Line Items] |
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| Cost |
211us-gaap_AvailableForSaleSecuritiesAmortizedCost / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_OtherDebtSecuritiesMember |
[4] |
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206us-gaap_AvailableForSaleSecuritiesAmortizedCost / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_OtherDebtSecuritiesMember |
| Gross Unrealized Gains |
9us-gaap_AvailableForSaleSecuritiesGrossUnrealizedGains / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_OtherDebtSecuritiesMember |
[4] |
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7us-gaap_AvailableForSaleSecuritiesGrossUnrealizedGains / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_OtherDebtSecuritiesMember |
| Gross Unrealized Loss |
(8)us-gaap_AvailableForSaleSecuritiesGrossUnrealizedLoss / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_OtherDebtSecuritiesMember |
[4] |
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(6)us-gaap_AvailableForSaleSecuritiesGrossUnrealizedLoss / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_OtherDebtSecuritiesMember |
| Estimated fair value |
212us-gaap_AvailableForSaleSecurities / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_OtherDebtSecuritiesMember |
[4] |
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207us-gaap_AvailableForSaleSecurities / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_OtherDebtSecuritiesMember |
| Equity Securities |
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| Schedule of Available-for-sale Securities [Line Items] |
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| Cost |
218us-gaap_AvailableForSaleSecuritiesAmortizedCost / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_EquitySecuritiesMember |
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215us-gaap_AvailableForSaleSecuritiesAmortizedCost / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_EquitySecuritiesMember |
| Gross Unrealized Gains |
452us-gaap_AvailableForSaleSecuritiesGrossUnrealizedGains / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_EquitySecuritiesMember |
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444us-gaap_AvailableForSaleSecuritiesGrossUnrealizedGains / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_EquitySecuritiesMember |
| Gross Unrealized Loss |
(4)us-gaap_AvailableForSaleSecuritiesGrossUnrealizedLoss / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_EquitySecuritiesMember |
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(4)us-gaap_AvailableForSaleSecuritiesGrossUnrealizedLoss / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_EquitySecuritiesMember |
| Estimated fair value |
666us-gaap_AvailableForSaleSecurities / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_EquitySecuritiesMember |
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655us-gaap_AvailableForSaleSecurities / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_EquitySecuritiesMember |
| Cash And Cash Equivalents |
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| Schedule of Available-for-sale Securities [Line Items] |
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| Cost |
19us-gaap_AvailableForSaleSecuritiesAmortizedCost / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CashAndCashEquivalentsMember |
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30us-gaap_AvailableForSaleSecuritiesAmortizedCost / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CashAndCashEquivalentsMember |
| Gross Unrealized Gains |
0us-gaap_AvailableForSaleSecuritiesGrossUnrealizedGains / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CashAndCashEquivalentsMember |
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1us-gaap_AvailableForSaleSecuritiesGrossUnrealizedGains / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CashAndCashEquivalentsMember |
| Gross Unrealized Loss |
0us-gaap_AvailableForSaleSecuritiesGrossUnrealizedLoss / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CashAndCashEquivalentsMember |
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0us-gaap_AvailableForSaleSecuritiesGrossUnrealizedLoss / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CashAndCashEquivalentsMember |
| Estimated fair value |
$ 19us-gaap_AvailableForSaleSecurities / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CashAndCashEquivalentsMember |
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$ 31us-gaap_AvailableForSaleSecurities / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CashAndCashEquivalentsMember |
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