Quarterly report pursuant to Section 13 or 15(d)

Short term and Long term Investments, 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, Restricted Deposits (Fair Value of Available-For-Sale Investments with Gross Unrealized Losses by Investment Type and Length of Time) (Details) - USD ($)
$ in Millions
Sep. 30, 2016
Dec. 31, 2015
Unrealized Losses    
Less Than 12 Months $ (4) $ (10)
12 Months or More (1) (2)
Fair Value    
Less Than 12 Months 737 1,248
12 Months or More 136 68
U.S. Treasury securities and obligations of U.S. government corporations and agencies    
Unrealized Losses    
Less Than 12 Months 0 (2)
12 Months or More 0 0
Fair Value    
Less Than 12 Months 4 294
12 Months or More 2 14
Corporate securities    
Unrealized Losses    
Less Than 12 Months (1) (6)
12 Months or More (1) (2)
Fair Value    
Less Than 12 Months 309 561
12 Months or More 80 41
Municipal securities    
Unrealized Losses    
Less Than 12 Months (1) (1)
12 Months or More 0 0
Fair Value    
Less Than 12 Months 231 208
12 Months or More 32 5
Asset-backed securities    
Unrealized Losses    
Less Than 12 Months 0 (1)
12 Months or More 0 0
Fair Value    
Less Than 12 Months 29 121
12 Months or More 21 8
Residential mortgage-backed securities    
Unrealized Losses    
Less Than 12 Months (1) 0
12 Months or More 0 0
Fair Value    
Less Than 12 Months 45 30
12 Months or More 0 0
Commercial mortgage-backed securities    
Unrealized Losses    
Less Than 12 Months (1) 0
12 Months or More 0 0
Fair Value    
Less Than 12 Months 119 34
12 Months or More $ 1 $ 0