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Fair Value Measurements (Schedule Of Carrying Values And Financial Instruments Not Carried At Fair Value) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	$ 511	$ 825	$ 1,001	$ 896
Cash and Cash Equivalents, Fair Value Disclosure	511	825
Short-term investments	445	443
Long-term investments	11	125
Current portion of long-term debt	449	0
Long-term debt	1,836	2,284
Carrying Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	445	443
Current portion of long-term debt	449	0
Long-term debt	1,836	2,284
Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	445	441
Current portion of long-term debt	466	0
Long-term debt	1,948	2,374
Cash [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	461	775
Cash and Cash Equivalents, Fair Value Disclosure	461	775
Time Deposits
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	50	50
Cash and Cash Equivalents, Fair Value Disclosure	50	50
Corporate Bonds \| Carrying Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	374	290
Long-term investments	11	125
Corporate Bonds \| Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	374	288
Long-term investments	11	125
Time Deposits \| Carrying Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	50	100
Time Deposits \| Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	50	100
Commercial Paper \| Carrying Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	21	53
Commercial Paper \| Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term investments	$ 21	$ 53