Capital Stock and Stock-Based Compensation Plans - Summary of Common Stock and Treasury Stock Activity (Details) - shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Summary Of Common Stock Activity [Roll Forward]
Common stock balance, January 1 (in shares)	874,701,118	883,108,963	892,738,518
Common stock acquired (in shares)	(18,786,897)	(19,185,828)	(19,271,304)
Shares issued for stock options (in shares)	6,040,920	9,670,988	8,536,639
Shares issued for restricted stock and other (in shares)	957,651	1,106,995	1,105,110
Common stock balance, December 31 (in shares)	862,912,792	874,701,118	883,108,963
Summary Of Treasury Stock Activity [Roll Forward]
Treasury stock balance, January 1 (in shares)	591,005,242	582,597,397	572,967,842
Common stock acquired (in shares)	18,786,897	19,185,828	19,271,304
Shares issued for stock options (in shares)	(6,040,920)	(9,670,988)	(8,536,639)
Shares issued for restricted stock and other (in shares)	(957,651)	(1,106,995)	(1,105,110)
Treasury stock balance, December 31 (in shares)	602,793,568	591,005,242	582,597,397