Computation of Earnings Per Share (Detail) - Common Share Equivalents Not Included in the Computation of Diluted EPS (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Earnings Per Share [Abstract]
Antidilutive common share equivalents as of December 31	0.3	0.3	0.7
Average market price per share of common stock during the year	$ 73.27	$ 57.50	$ 43.80