Shareholders' Equity (Summary of Shares Outstanding) (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Shareholders' Equity Note [Line Items]
Common Stock, Par or Stated Value Per Share	$ 1.667
Preferred stock without par value (in dollars per share)	$ 10,000,000
Shares of common stock authorized	1,200,000,000
Per share cash dividends paid (in dollars per share)	$ 2.10	$ 1.98	$ 1.86
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance (in shares)	235,680,470	235,861,434	251,174,399
Purchases (in shares)		(2,722,800)	(15,877,364)
Issuances (in shares)	1,005,795	2,541,836	564,399
Ending balance (in shares)	236,686,265	235,680,470	235,861,434
Common Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance (in shares)	581,146,136	581,146,136	581,146,136
Ending balance (in shares)	581,146,136	581,146,136	581,146,136
Treasury Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance (in shares)	345,465,666	345,284,702	329,971,737
Purchases (in shares)		(2,722,800)	(15,877,364)
Issuances (in shares)	1,005,795	2,541,836	564,399
Ending balance (in shares)	344,459,871	345,465,666	345,284,702