Activity in Number of Shares of Common Stock Issued and Outstanding (Detail)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Reconciliation of Common Stock Outstanding [Line Items]
At beginning of year	192,836,008	191,115,378	190,713,806
Stock options exercised	615,674	1,495,926	548,659
Employee stock purchase and thrift plans	33,390	49,657	61,575
Restricted stock awards, net of forfeitures	238,136	175,047	(208,662)
At end of year	193,723,208	192,836,008	191,115,378