Stock Option Activity (Detail) (USD $)	12 Months Ended
	Dec. 31, 2011 Year
Shares
Beginning Balance	7,967,416
Granted	817,707
Exercised	(839,886)
Forfeited	(45,203)
Expired	(62,338)
Ending Balance	7,837,696
Options exercisable at end of period	5,694,049
Options expected to vest at end of period	2,107,848
Weighted Average Exercise Price
Beginning Balance	$ 31.34
Granted	$ 36.73
Exercised	$ 25.03
Forfeited	$ 32.86
Expired	$ 40.06
Ending Balance	$ 32.50
Options exercisable at end of period	$ 32.38
Options expected to vest at end of period	$ 32.82
Weighted Average Remaining Contractual Life
Balance at end of period	5.6
Options exercisable at end of period	4.6
Options expected to vest at end of period	8.2
Aggregate Intrinsic value
Balance at end of period	$ 20,161,647
Options exercisable at end of period	16,052,331
Options expected to vest at end of period	$ 4,109,316