Stockholders' Equity (Shares Outstanding) (Details) - shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Shares Outstanding [Roll Forward]
Balance at beginning of year (in shares)	574,128,911	571,803,838	575,183,072
Stock options exercised (in shares)	1,630,664	2,325,073	620,766
Purchases of common stock (in shares)	(1,600,000)	0	(4,000,000)
Balance at end of year (in shares)	574,159,575	574,128,911	571,803,838