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)