Annual report pursuant to Section 13 and 15(d)

Assets And Liabilities Measured At Fair Value (Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details)

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Assets And Liabilities Measured At Fair Value (Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) - USD ($)
$ in Millions
Dec. 31, 2017
Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash equivalents $ 655 $ 625
Available-for-sale securities 2,275 1,846
Investments in and Advances to Affiliates, at Fair Value 3,635 3,161
Debt 1,846 1,667
Level 1    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Cash equivalents 655 625
Available-for-sale securities 2,275 1,846
Investments in and Advances to Affiliates, at Fair Value 3,635 3,161
Significant Other Observable Inputs (Level 2)    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Debt $ 1,846 $ 1,667