Supplementary Financial Statement Information (Schedule Of Interest Income And Interest Expense) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Disclosure Text Block Supplement [Abstract]
Interest expense (a)	$ 758	$ 695	$ 644
Interest income (a)	186	175	89
Capitalized interest costs	$ 25	$ 28	$ 25