Income Taxes - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
Oct. 31, 2011	Oct. 31, 2010	Oct. 31, 2011	Oct. 31, 2010
Income Taxes [Line Items]
Effective tax rates	20.00%	25.00%	21.00%	24.00%
Discrete tax (benefit) expense related to stock-based compensation expense	$ 3.3		$ 7.8
Effective tax rate excluding the impact of discrete tax items	24.00%		24.00%
Federal statutory tax rate	35.00%
Gross unrecognized tax benefits	198.3		198.3
Amount of gross unrecognized tax benefits that would impact the effective tax rate, if recognized	184.3		184.3
Net deferred tax assets	$ 172.9		$ 172.9

For entities that net deferred tax assets and tax liabilities, represents the unclassified net amount of deferred tax assets and liabilities as of the balance sheet date, which result from applying the applicable enacted tax rate to net temporary differences and carryforwards pertaining to assets or liabilities. A temporary difference is a difference between the tax basis of an asset or liability and its carrying amount in the financial statements prepared in accordance with generally accepted accounting principles that will reverse in ensuing periods.

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A ratio calculated by dividing the reported amount of income tax expense attributable to continuing operations for the period by GAAP-basis pretax income from continuing operations.

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- Definition

The domestic federal statutory tax rate applicable under enacted tax laws to the Company's pretax income from continuing operations for the period. The "statutory" tax rate is the regular tax rate if there are alternative tax systems.

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