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
Mar. 31, 2019
Dec. 31, 2018
Unrealized Losses    
Less Than 12 Months $ (6) $ (36)
12 Months or More (25) (55)
Fair Value    
Fair Value, Less Than 12 Months 772 2,555
Fair Value, 12 Months or More 2,244 2,420
U.S. Treasury securities and obligations of U.S. government corporations and agencies    
Unrealized Losses    
Less Than 12 Months 0 0
12 Months or More (1) (2)
Fair Value    
Fair Value, Less Than 12 Months 1 59
Fair Value, 12 Months or More 172 202
Corporate securities    
Unrealized Losses    
Less Than 12 Months (4) (27)
12 Months or More (12) (25)
Fair Value    
Fair Value, Less Than 12 Months 392 1,389
Fair Value, 12 Months or More 1,010 871
Municipal securities    
Unrealized Losses    
Less Than 12 Months 0 (4)
12 Months or More (3) (14)
Fair Value    
Fair Value, Less Than 12 Months 74 591
Fair Value, 12 Months or More 496 806
Asset-backed securities    
Unrealized Losses    
Less Than 12 Months (2) (2)
12 Months or More (1) (2)
Fair Value    
Fair Value, Less Than 12 Months 221 318
Fair Value, 12 Months or More 196 168
Residential mortgage-backed securities    
Unrealized Losses    
Less Than 12 Months 0 (1)
12 Months or More (6) (8)
Fair Value    
Fair Value, Less Than 12 Months 12 61
Fair Value, 12 Months or More 241 233
Commercial mortgage-backed securities    
Unrealized Losses    
Less Than 12 Months 0 (2)
12 Months or More (2) (4)
Fair Value    
Fair Value, Less Than 12 Months 72 137
Fair Value, 12 Months or More $ 129 $ 140