Cash and Marketable Securities (Schedule Of Proceeds And Gross Realized Gains Resulting From Sales Of Available-For-Sale Securities And Gross Realized Losses)(Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Cash and Marketable Securities [Abstract]
Proceeds from sale of securities	$ 42	$ 20	$ 42	$ 20
Gross realized gains, pre-tax	4	6	4	6
Gross realized gains, net of tax	$ 2	$ 4	$ 2	$ 4