(Stock-Based Compensation Expense And Related Income Tax Benefits) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Income tax benefits related to stock-based compensation	$ 17	$ 30	$ 16
Selling And Marketing Expense [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense (included in selling and administrative expense)	$ 72	$ 130	$ 135