Stockholders' Equity (Schedule of Treasury Stock) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		158 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021
Class of Stock [Line Items]
Shares repurchased	1,831,970	1,709,431	64,600,021
Average purchase price per share	$ 136.47	$ 87.87	$ 78.22
Shares repurchased (in $ millions)	$ 250	$ 150	$ 5,053
Aggregate Board of Directors repurchase authorizations (in $ millions)	$ 0	$ 0	$ 5,866