Shareholders' Equity (Summary of Shares Outstanding) (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
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)	$ 1.7	$ 1.56	$ 1.41
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance (in shares)	257,330,160	266,876,009	271,964,566
Purchases (in shares)	(7,427,557)	(10,725,869)	(6,992,772)
Issuances (in shares)	1,271,796	1,180,020	1,904,215
Ending balance (in shares)	251,174,399	257,330,160	266,876,009
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)	323,815,976	314,270,127	309,181,570
Purchases (in shares)	(7,427,557)	(10,725,869)	(6,992,772)
Issuances (in shares)	1,271,796	1,180,020	1,904,215
Ending balance (in shares)	329,971,737	323,815,976	314,270,127