Stock-Based Compensation - Weighted Average Assumptions Used To Value Employee Stock Options Granted (Detail)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Stock Based Compensation [Line Items]
Expected option life	5 years 6 months	5 years 4 months 24 days	5 years 8 months 12 days
Expected volatility	24.20%	24.20%	24.80%
Expected dividend yield	4.10%	3.70%	3.80%
Risk-free interest rate	1.10%	2.30%	2.90%