Fair Value Measurements (Schedule Of Carrying Values And Financial Instruments Not Carried At Fair Value) (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Current portion of long-term debt	$ 449	$ 485
Long-term Debt, Excluding Current Maturities	2,281	2,728
Reported Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	1,726	1,906
Current portion of long-term debt	449	485
Long-term Debt, Excluding Current Maturities	2,281	2,728
Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments	1,723	1,901
Current portion of long-term debt	468	490
Long-term Debt, Excluding Current Maturities	$ 2,490	$ 2,956