Share-Based Compensation - Stock Options Assumptions Table (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Weighted-average grant-date fair value	$ 23.55	$ 26.27	$ 25.84
Assumptions
Expected option life—years	4 years 10 months 24 days	4 years 9 months 18 days	4 years 10 months 24 days
Volatility	29.90%	33.90%	44.20%
Risk-free interest rate	1.60%	1.30%	0.70%
Dividend yield	1.10%	0.80%	0.50%