Revenue Recognition (Changes In Contract Assets And Contract Liabilities) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Revenue Recognition [Abstract]
Contract current assets, Beginning balance	$ 37	$ 44
Contract current assets, Revenue recognized included in opening contract balance	(9)	(10)
Contract current assets, Credits granted, excluding amounts recognized as revenue	1	11
Contract current assets, Ending balance	29	45
Contract noncurrent assets, Beginning balance	8	25
Contract noncurrent assets, Revenue recognized included in opening contract balance		(4)
Contract noncurrent assets, Credits granted, excluding amounts recognized as revenue		1
Contract current assets, Ending balance	8	22
Contract current liabilities, Beginning balance	41	49
Contract current liabilities, Revenue recognized included in opening contract balance	(21)	(20)
Contract current liabilities, Cash received, excluding amounts recognized as revenue	25	18
Contract current liabilities, Reclassified between Current and NonCurrent, NonCurrent	1
Contract current liabilities, Ending balance	46	47
Contract noncurrent liabilities, Beginning balance	21	22
Contract noncurrent liabilities, Revenue recognized included in opening contract balance	(4)	(5)
Contract noncurrent liabilities, Cash received, excluding amounts recognized as revenue	5	3
Contract current liabilities, Reclassified between Current and NonCurrent	(1)
Contract noncurrent liabilities, Ending balance	$ 21	$ 20