Quarterly report pursuant to Section 13 or 15(d)

Short-Term And Long-Term Investments And Restricted Deposits (Fair Value Of Available-For-Sale Investments With Gross Unrealized Losses By Investment Type And Length Of Time) (Details)

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Short-Term And Long-Term Investments And Restricted Deposits (Fair Value Of Available-For-Sale Investments With Gross Unrealized Losses By Investment Type And Length Of Time) (Details) - USD ($)
$ in Millions
Jun. 30, 2016
Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]    
Unrealized losses, less than 12 months $ (4) $ (10)
Fair value, less than 12 months 492 1,248
Unrealized losses, 12 months or more 0 (2)
Fair value, 12 months or more 126 68
U.S. Treasury securities and obligations of U.S. government corporations and agencies    
Schedule of Available-for-sale Securities [Line Items]    
Unrealized losses, less than 12 months 0 (2)
Fair value, less than 12 months 2 294
Unrealized losses, 12 months or more 0 0
Fair value, 12 months or more 0 14
Corporate securities    
Schedule of Available-for-sale Securities [Line Items]    
Unrealized losses, less than 12 months (1) (6)
Fair value, less than 12 months 228 561
Unrealized losses, 12 months or more 0 (2)
Fair value, 12 months or more 80 41
Municipal securities    
Schedule of Available-for-sale Securities [Line Items]    
Unrealized losses, less than 12 months (1) (1)
Fair value, less than 12 months 76 208
Unrealized losses, 12 months or more 0 0
Fair value, 12 months or more 30 5
Asset-backed securities    
Schedule of Available-for-sale Securities [Line Items]    
Unrealized losses, less than 12 months (1) (1)
Fair value, less than 12 months 83 121
Unrealized losses, 12 months or more 0 0
Fair value, 12 months or more 6 8
Residential mortgage-backed securities    
Schedule of Available-for-sale Securities [Line Items]    
Unrealized losses, less than 12 months (1) 0
Fair value, less than 12 months 39 30
Unrealized losses, 12 months or more 0 0
Fair value, 12 months or more 0 0
Commercial mortgage-backed securities    
Schedule of Available-for-sale Securities [Line Items]    
Unrealized losses, less than 12 months 0 0
Fair value, less than 12 months 64 34
Unrealized losses, 12 months or more 0 0
Fair value, 12 months or more $ 10 $ 0