Quarterly report pursuant to Section 13 or 15(d)

Short term and Long term Investments, Restricted Deposits (Contractual Maturities of Short-Term and Long-Term Investments and Restricted Deposits) (Details)

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Short term and Long term Investments, Restricted Deposits (Contractual Maturities of Short-Term and Long-Term Investments and Restricted Deposits) (Details) - USD ($)
$ in Millions
Sep. 30, 2016
Dec. 31, 2015
Investments    
Schedule of Available-for-sale Securities [Line Items]    
Amortized cost, one year or less $ 406 $ 176
Amortized cost, one year through five years 1,978 1,662
Amortized cost, five years through ten years 1,098 267
Amortized cost, greater than ten years 577 5
Amortized cost, asset-backed securities 845 0
Amortized cost, total 4,904 2,110
Fair value, one year or less 406 176
Fair value, one year through five years 2,000 1,654
Fair value, five years through ten years 1,116 268
Fair value, greater than ten years 589 5
Fair value, asset-backed securities 863 0
Fair value, total 4,974 2,103
Restricted Deposits    
Schedule of Available-for-sale Securities [Line Items]    
Amortized cost, one year or less 122 93
Amortized cost, one year through five years 14 22
Amortized cost, five years through ten years 0 0
Amortized cost, greater than ten years 0 0
Amortized cost, asset-backed securities 0 0
Amortized cost, total 136 115
Fair value, one year or less 123 93
Fair value, one year through five years 14 22
Fair value, five years through ten years 0 0
Fair value, greater than ten years 0 0
Fair value, asset-backed securities 0 0
Fair value, total $ 137 $ 115