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	Mar. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Amortized cost of securities	$ 12	$ 13
Fair value of securities	12	13
Debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized cost of debt securities	4	4
Fair value of debt securities	4	4
Equity securities
Debt Securities, Available-for-sale [Line Items]
Amortized cost of equity securities	8	9
Fair value of equity securities	$ 8	$ 9