Debt (Estimated Fair Value Of Significant Financial Instruments) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Estimate of Fair Value Measurement
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term debt	$ 313	$ 12
Long-term debt	4,625	4,513
Reported Value Measurement
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term debt	312	12
Long-term debt	$ 4,495	$ 4,402