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Summary Of Significant Accounting Policies Cash and Equivalents and Investments in Debt and Equity Securities (Details) (USD $)
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Cash and Equivalents and Investments in Debt and Equity Securities [Abstract]      
Trading Securities $ 0us-gaap_TradingSecurities    
(Purchases) proceeds of other securities (497,000,000)us-gaap_PaymentsForProceedsFromInvestments (22,000,000)us-gaap_PaymentsForProceedsFromInvestments 219,000,000us-gaap_PaymentsForProceedsFromInvestments
Payments to Acquire Held-to-maturity Securities 500,000,000us-gaap_PaymentsToAcquireHeldToMaturitySecurities 0us-gaap_PaymentsToAcquireHeldToMaturitySecurities 260,000,000us-gaap_PaymentsToAcquireHeldToMaturitySecurities
Maturities of held-to-maturity securities     224,000,000us-gaap_ProceedsFromMaturitiesPrepaymentsAndCallsOfHeldToMaturitySecurities
Proceeds from Sale of Held-to-maturity Securities     $ 211,000,000us-gaap_ProceedsFromSaleOfHeldToMaturitySecurities