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	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 19	$ 13
Gross Realized and Unrealized Gains	1
Fair Value	21	13
Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	4	4
Fair Value	4	4
Equity Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	15	9
Gross Realized and Unrealized Gains	1
Fair Value	$ 16	$ 9