Weighted-Average Assumptions (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Accounting Policies [Abstract]
Expected dividend yield	2.80%	3.20%	3.50%
Expected stock price volatility	20.80%	21.50%	22.10%
Risk-free interest rate	1.10%	2.80%	2.80%
Expected life of options In years	6 years 1 month 6 days	6 years 3 months 18 days	6 years 2 months 12 days
Fair value per option granted	$ 13.65	$ 12.18	$ 9.90