Revenue Recognition (Changes In Contract Assets And Contract Liabilities) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Revenue Recognition [Abstract]
Contract current assets, Beginning balance	$ 6	$ 37
Contract current assets, Revenue recognized included in opening contract balance	(4)	(9)
Contract current assets, Credits granted, excluding amounts recognized as revenue		1
Contract current assets, Ending balance	2	29
Contract noncurrent assets, Beginning balance	9	8
Contract noncurrent assets, Ending balance	9	8
Contract current liabilities, Beginning balance	58	41
Contract current liabilities, Revenue recognized included in opening contract balance	(17)	(21)
Contract current liabilities, Cash received, excluding amounts recognized as revenue	17	25
Contract current liabilities, Reclassified between Current and NonCurrent		1
Contract current liabilities, Ending balance	58	46
Contract noncurrent liabilities, Beginning balance	20	21
Contract noncurrent liabilities, Revenue recognized included in opening contract balance	(2)	(4)
Contract noncurrent liabilities, Cash received, excluding amounts recognized as revenue	1	5
Contract noncurrent liabilities, Reclassified between Current and NonCurrent		(1)
Contract noncurrent liabilities, Ending balance	$ 19	$ 21