Assumptions Used To Determine Compensation Expense for Management Stock Purchase Program (Detail) (Management Stock Purchase Plan, USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Management Stock Purchase Plan
Share Based Compensation [Line Items]
Dividend yield	0.90%	0.80%	0.90%
Risk-free interest rate	0.16%	0.12%	0.22%
Expected life in years	7 months 6 days	7 months 6 days	7 months 6 days
Expected volatility	20.00%	16.00%	20.00%
Fair value	$ 38.33	$ 38.25	$ 27.42