Employee Benefit Plans (Assumptions to Determine Fair Value of Options Granted) (Detail)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Share Based Payment Award Stock Options Valuation Assumptions [Line Items]
Expected term, Years	6 years 6 months	6 years 3 months 18 days	6 years
Risk-free interest rate, minimum	0.10%	0.01%	0.14%
Risk-free interest rate, maximum	3.58%	3.91%	4.98%
Weighted-average risk-free interest rate	1.85%	2.23%	2.79%
Dividend yield	3.28%	2.84%	2.79%
Expected market price volatility, minimum	24.97%	24.87%	31.11%
Expected market price volatility, maximum	31.15%	31.32%	41.40%
Weighted-average expected market price volatility	28.06%	29.43%	34.65%
Minimum [Member]
Share Based Payment Award Stock Options Valuation Assumptions [Line Items]
Expected term, Years	6 years	6 years	5 years 7 months 6 days
Maximum [Member]
Share Based Payment Award Stock Options Valuation Assumptions [Line Items]
Expected term, Years	6 years 10 months 24 days	7 years	6 years 10 months 24 days