Quarterly report pursuant to Section 13 or 15(d)

Short-Term And Long-Term Investments And Restricted Deposits (By Investment Type) (Details)

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Short-Term And Long-Term Investments And Restricted Deposits (By Investment Type) (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2016
Jun. 30, 2015
Jun. 30, 2016
Jun. 30, 2015
Dec. 31, 2015
Schedule Of Investments And Restricted Deposits By Type [Line Items]          
Amortized Cost $ 4,742   $ 4,742   $ 2,225
Gross Unrealized Gains 72   72   5
Gross Unrealized Losses (4)   (4)   (12)
Fair Value 4,810   4,810   2,218
Discontinued operations, net of income tax benefit (1) $ 0 (2) $ (1)  
U.S. Treasury securities and obligations of U.S. government corporations and agencies          
Schedule Of Investments And Restricted Deposits By Type [Line Items]          
Amortized Cost 293   293   431
Gross Unrealized Gains 3   3   0
Gross Unrealized Losses 0   0   (2)
Fair Value 296   296   429
Corporate securities          
Schedule Of Investments And Restricted Deposits By Type [Line Items]          
Amortized Cost 1,885   1,885   859
Gross Unrealized Gains 28   28   2
Gross Unrealized Losses (1)   (1)   (8)
Fair Value 1,912   1,912   853
Restricted certificates of deposit          
Schedule Of Investments And Restricted Deposits By Type [Line Items]          
Amortized Cost 5   5   5
Gross Unrealized Gains 0   0   0
Gross Unrealized Losses 0   0   0
Fair Value 5   5   5
Restricted cash equivalents          
Schedule Of Investments And Restricted Deposits By Type [Line Items]          
Amortized Cost 73   73   78
Gross Unrealized Gains 0   0   0
Gross Unrealized Losses 0   0   0
Fair Value 73   73   78
Municipal securities          
Schedule Of Investments And Restricted Deposits By Type [Line Items]          
Amortized Cost 1,520   1,520   496
Gross Unrealized Gains 33   33   2
Gross Unrealized Losses (1)   (1)   (1)
Fair Value 1,552   1,552   497
Asset-backed securities          
Schedule Of Investments And Restricted Deposits By Type [Line Items]          
Amortized Cost 298   298   163
Gross Unrealized Gains 2   2   0
Gross Unrealized Losses (1)   (1)   (1)
Fair Value 299   299   162
Residential mortgage-backed securities          
Schedule Of Investments And Restricted Deposits By Type [Line Items]          
Amortized Cost 197   197   66
Gross Unrealized Gains 3   3   1
Gross Unrealized Losses (1)   (1)   0
Fair Value 199   199   67
Commercial mortgage-backed securities          
Schedule Of Investments And Restricted Deposits By Type [Line Items]          
Amortized Cost 320   320   40
Gross Unrealized Gains 3   3   0
Gross Unrealized Losses 0   0   0
Fair Value 323   323   40
Cost and equity method investments          
Schedule Of Investments And Restricted Deposits By Type [Line Items]          
Amortized Cost 135   135   71
Gross Unrealized Gains 0   0   0
Gross Unrealized Losses 0   0   0
Fair Value 135   135   71
Life insurance contracts          
Schedule Of Investments And Restricted Deposits By Type [Line Items]          
Amortized Cost 16   16   16
Gross Unrealized Gains 0   0   0
Gross Unrealized Losses 0   0   0
Fair Value $ 16   $ 16   $ 16