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 |