Computation of Weighted Average Shares Outstanding (Detail) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Earnings Per Share Disclosure [Line Items]
Basic	111.1	127.3
Dilutive share-based awards		0.9	[1]
Diluted	111.1	128.2

[1] The three months ended March 31, 2013 excludes 0.8 million potentially dilutive share-based awards as their effect would be antidilutive.