Summary of Option Activity (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding at December 31, 2011, Options			8.3
Granted, Options	0	0	1.5	1.1
Exercised, Options			(1.1)
Cancelled, Options			(0.1)
Outstanding at September 30, 2012, Options	8.6		8.6
Exercisable at September 30, 2012, Options	4.7		4.7
Outstanding at December 31, 2011, Weighted-Average Exercise Price			$ 26.39
Granted, Weighted-Average Exercise Price			$ 53.79
Exercised, Weighted-Average Exercise Price			$ 18.09
Cancelled, Weighted-Average Exercise Price			$ 32.56
Outstanding at September 30, 2012, Weighted-Average Exercise Price	$ 32.31		$ 32.31
Exercisable at September 30, 2012, Weighted-Average Exercise Price	$ 23.05		$ 23.05
Outstanding at September 30, 2012, Weighted-Average Remaining Contractual Term, years			6 years 3 months 18 days
Exercisable at September 30, 2012, Weighted-Average Remaining Contractual Term, years			4 years 7 months 6 days
Outstanding at September 30, 2012, Aggregate Intrinsic Value	$ 186.0		$ 186.0
Exercisable at September 30, 2012, Aggregate Intrinsic Value	$ 146.4		$ 146.4

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Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of vested portions of options outstanding and currently exercisable.

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The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

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Weighted average remaining contractual term for vested portions of options outstanding and currently exercisable or convertible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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For presentations that combine terminations, the number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan or that expired.

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Weighted average price of options that were either forfeited or expired.

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Net number of share options (or share units) granted during the period.

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Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of options outstanding.

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The number of shares reserved for issuance under stock option agreements awarded under the plan that validly exist and are outstanding as of the balance sheet date, including vested options.

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Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Number of share options (or share units) exercised during the current period.

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