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Fair Value Measurements (Details Textuals) - USD ($)
$ in Millions
 9 Months Ended
Sep. 30, 2016
Dec. 31, 2015
Fair Value of Financial Instruments [Line Items]    
Investment excludes receivables, payables and accrued income $ (8) $ 7
Cash balance excluded from available for sale securities 50 157
Investments not required to be disclosed $ 276 255
NUG contracts    
Fair Value of Financial Instruments [Line Items]    
Period of future observable data to determine contract price 3 years  
FES    
Fair Value of Financial Instruments [Line Items]    
Investment excludes receivables, payables and accrued income $ 1 1
Cash balance excluded from available for sale securities $ 39 $ 139