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Derivative Instruments, Hedging Activities and Fair Value Measurements, Other Fair Value Measurements (Details) (USD $)
In Billions, unless otherwise specified
Sep. 30, 2013
Dec. 31, 2012
Carrying Value [Member]
   
Financial Liabilities: [Abstract]    
Fixed Rate Debt Principal Amount Fair Value Disclosure $ 17.43 $ 16.18
Level 2 [Member] | Fair Value [Member]
   
Financial Liabilities: [Abstract]    
Fixed Rate Debt Principal Amount Fair Value Disclosure $ 18.42 $ 18.42