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Cash and Marketable Securities (Schedule Of Amortized Cost, Fair Value And Gross Unrealized Gains And Losses Of The Company's Short- And Long-Term Investments In Debt And Equity Securities) (Details) - USD ($)
$ in Millions
Dec. 31, 2018
Dec. 31, 2017
Cash and Marketable Securities [Abstract]    
Amortized cost of debt securities $ 9 $ 25
Fair value of debt securities 9 25
Amortized cost of equity securities   2
Fair value of equity securities   2
Amortized cost of securities 9 27
Fair value of securities $ 9 $ 27