Stockholders' Equity (Schedule of Treasury Stock) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended				155 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018		Dec. 31, 2020
Stockholders' Equity Note [Abstract]
Shares reacquired under clawback agreement			1,700
Shares repurchased	5,889,073	9,166,267	7,933,692	[1]	62,768,051
Average purchase price per share	$ 110.41	$ 109.10	$ 103.01		$ 76.52
Amount spent on repurchased shares (in millions)	$ 650	$ 1,000	$ 817		$ 4,803
Aggregate Board of Directors repurchase authorizations during the period	500	$ 1,500	$ 0
Share repurchase plan, authorized repurchase amount	$ 5,866				$ 5,866

[1] Excludes 1,700 common shares reacquired pursuant to an employee clawback agreement.