Summary of Stock Option Activity (Detail) (Employee Stock Option, USD $) In Millions, except Share data in Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2013
Employee Stock Option
Shares
Outstanding at December 31, 2012, shares	2,766
Granted, shares	755
Exercised, shares	(432)
Forfeited and expired, shares	(230)
Outstanding at Sep 30, 2013, shares	2,859
Expected to vest at Sep 30, 2013, shares	1,341
Exercisable at Sep 30, 2013, shares	1,483
Weighted-Average Exercise Price
Outstanding at December 31, 2012, Weighted-Average Exercise Price	$ 35.50
Granted, Weighted-Average Exercise Price	$ 23.64
Exercised, Weighted-Average Exercise Price	$ 10.47
Forfeited and expired, Weighted-Average Exercise Price	$ 76.10
Outstanding at Sep 30, 2013, Weighted-Average Exercise Price	$ 32.84
Expected to vest at Sep 30, 2013, Weighted-Average Exercise Price	$ 24.39
Exercisable at Sep 30, 2013, Weighted-Average Exercise Price	$ 40.72
Weighted-Average Remaining Contractual Term
Outstanding at Sep 30, 2013, Weighted-Average Remaining Contractual Term	2 years 7 months 28 days
Expected to vest at Sep 30, 2013, Weighted-Average Remaining Contractual Term	3 years 9 months 7 days
Exercisable at Sep 30, 2013, Weighted-Average Remaining Contractual Term	1 year 7 months 17 days
Aggregate Intrinsic Value
Outstanding at Sep 30, 2013, Aggregate Intrinsic Value	$ 9.4
Expected to vest at Sep 30, 2013, Aggregate Intrinsic Value	3.6
Exercisable at Sep 30, 2013, Aggregate Intrinsic Value	$ 5.8