Revenues (Movement In Deferred Revenue) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Revenues[Abstract]
Balance at beginning of period	$ 101	$ 101
Deferral of revenue	133	149
Recognition of deferred revenue	(134)	(149)
Balance at end of period	$ 101	$ 101