Debt (Estimated Fair Value Of Significant Financial Instruments) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term debt	$ 517	$ 1,215
Long-term debt	10,796	10,741
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term debt	523	1,229
Long-term debt	$ 12,858	$ 11,953