Revenue Recognition (Changes In Contract Assets And Contract Liabilities) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Revenue Recognition [Abstract]
Contract current assets, Beginning balance	$ 44	$ 40
Contract current assets, Revenue recognized included in opening contract balance	(10)	(11)
Contract current assets, Credits granted, excluding amounts recognized as revenue	11	10
Contract current assets, Ending balance	45	39
Contract noncurrent assets, Beginning balance	25	37
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	22	37
Contract current liabilities, Beginning balance	49	41
Contract current liabilities, Revenue recognized included in opening contract balance	(20)	(20)
Contract current liabilities, Cash received, excluding amounts recognized as revenue	18	26
Contract current liabilities, Ending balance	47	47
Contract noncurrent liabilities, Beginning balance	22	19
Contract noncurrent liabilities, Revenue recognized included in opening contract balance	(5)	(4)
Contract noncurrent liabilities, Cash received, excluding amounts recognized as revenue	3	4
Contract noncurrent liabilities, Ending balance	$ 20	$ 19