Summary of Option Activity (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012
Options
Shares, Outstanding, Beginning Balance	17.4
Shares, Granted	0.5
Shares, Exercised	(4.4)
Shares, Forfeited	(0.1)
Shares, Expired	(0.4)
Shares, Outstanding, Ending Balance	13.0
Shares, Vested and expected to vest	12.8
Shares, Exercisable	10.4
Options
Weighted Average Exercise Price Per Share, Outstanding Beginning Balance	$ 39.60
Weighted Average Exercise Price Per Share, Granted	$ 38.68
Weighted Average Exercise Price Per Share, Exercised	$ 28.77
Weighted Average Exercise Price Per Share, Forfeited	$ 27.66
Weighted Average Exercise Price Per Share, Expired	$ 57.28
Weighted Average Exercise Price Per Share, Outstanding Ending Balance	$ 42.82
Weighted Average Exercise Price Per Share, Vested and expected to vest	$ 43.05
Weighted Average Exercise Price Per Share, Exercisable	$ 46.14
Weighted Average Remaining Contractual Term
Weighted Average Remaining Contractual Term, Outstanding	4 years 7 months 6 days
Weighted Average Remaining Contractual Term, Vested and expected to vest	4 years 6 months
Weighted Average Remaining Contractual Term	3 years 10 months 24 days
Aggregate Intrinsic Value
Aggregate Intrinsic Value, Outstanding	$ 163.9
Aggregate Intrinsic Value, Vested and expected to vest	159.2
Aggregate Intrinsic Value, Exercisable	$ 109.9