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
Jun. 30, 2015
Dec. 31, 2014
Schedule Of Investments And Restricted Deposits By Type [Line Items]    
Amortized Cost $ 1,781 $ 1,556
Gross Unrealized Gains 5 5
Gross Unrealized Losses (4) (4)
Fair Value 1,782 1,557
U.S. Treasury Securities And Obligations Of U.S. Government Corporations And Agencies [Member]    
Schedule Of Investments And Restricted Deposits By Type [Line Items]    
Amortized Cost 451 393
Gross Unrealized Gains 1 1
Gross Unrealized Losses (1) (2)
Fair Value 451 392
Corporate Securities [Member]    
Schedule Of Investments And Restricted Deposits By Type [Line Items]    
Amortized Cost 632 556
Gross Unrealized Gains 2 2
Gross Unrealized Losses (2) (2)
Fair Value 632 556
Restricted Certificates Of Deposit [Member]    
Schedule Of Investments And Restricted Deposits By Type [Line Items]    
Amortized Cost 6 6
Gross Unrealized Gains 0 0
Gross Unrealized Losses 0 0
Fair Value 6 6
Restricted Cash Equivalents [Member]    
Schedule Of Investments And Restricted Deposits By Type [Line Items]    
Amortized Cost 80 79
Gross Unrealized Gains 0 0
Gross Unrealized Losses 0 0
Fair Value 80 79
Municipal Securities, General Obligation [Member]    
Schedule Of Investments And Restricted Deposits By Type [Line Items]    
Amortized Cost 96 54
Gross Unrealized Gains 0 0
Gross Unrealized Losses 0 0
Fair Value 96 54
Municipal Securities, Pre-Refunded [Member]    
Schedule Of Investments And Restricted Deposits By Type [Line Items]    
Amortized Cost 4 5
Gross Unrealized Gains 0 0
Gross Unrealized Losses 0 0
Fair Value 4 5
Municipal Securities, Revenue [Member]    
Schedule Of Investments And Restricted Deposits By Type [Line Items]    
Amortized Cost 161 101
Gross Unrealized Gains 1 1
Gross Unrealized Losses (1) 0
Fair Value 161 102
Municipal Securities, Variable Rate Demand Notes [Member]    
Schedule Of Investments And Restricted Deposits By Type [Line Items]    
Amortized Cost 28 14
Gross Unrealized Gains 0 0
Gross Unrealized Losses 0 0
Fair Value 28 14
Asset Backed Securities [Member]    
Schedule Of Investments And Restricted Deposits By Type [Line Items]    
Amortized Cost 162 180
Gross Unrealized Gains 0 0
Gross Unrealized Losses 0 0
Fair Value 162 180
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]    
Schedule Of Investments And Restricted Deposits By Type [Line Items]    
Amortized Cost 77 84
Gross Unrealized Gains 1 1
Gross Unrealized Losses 0 0
Fair Value 78 85
Cost And Equity Method Investments [Member]    
Schedule Of Investments And Restricted Deposits By Type [Line Items]    
Amortized Cost 68 68
Gross Unrealized Gains 0 0
Gross Unrealized Losses 0 0
Fair Value 68 68
Life Insurance Contracts [Member]    
Schedule Of Investments And Restricted Deposits By Type [Line Items]    
Amortized Cost 16 16
Gross Unrealized Gains 0 0
Gross Unrealized Losses 0 0
Fair Value $ 16 $ 16