Assumptions Used To Determine Compensation Expense for Management Stock Purchase Program (Detail) (Management Stock Purchase Plan, USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Management Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dividend yield	0.60%	0.80%	0.90%
Risk-free interest rate	0.07%	0.10%	0.16%
Expected life in years	7 months 6 days	7 months 6 days	7 months 6 days
Expected volatility	20.00%	15.00%	20.00%
Fair value	$ 51.82	$ 37.20	$ 38.33