Equity Incentive Plans, Stock Options Outstanding (Details) (USD $) In Millions, except Share data in Thousands, unless otherwise specified	3 Months Ended	6 Months Ended
Sep. 30, 2011	Sep. 30, 2011	Sep. 30, 2010
Summary of information about stock options outstanding [Line Items]
Total intrinsic value of options exercised related to stock incentive plans	$ 1.1	$ 13.1
Aggregate intrinsic value of options outstanding related to stock incentive plans	27.6	27.6
Aggregate intrinsic value of options exercisable related to stock incentive plans	$ 27.6	$ 27.6
Closing price of company's common stock related to calculation of aggregate intrinsic value of stock options (in dollars per share)	$ 31.11
Exercisable number of option shares (in shares)	4,566,785	4,566,785	7,493,700
Weighted average exercise price per share of exercisable options (in dollars per share)	$ 25.17	$ 25.17	$ 24.74

Closing price per share of company's common stock at balance sheet date

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The total dollar difference between fair values of the underlying shares reserved for issuance and exercise prices of vested portions of options outstanding and currently exercisable under the option plan as of the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

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The total accumulated difference between fair values of underlying shares on dates of exercise and exercise price on options which were exercised (or share units converted) into shares during the reporting period under the plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

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The total dollar difference between fair values of the underlying shares reserved for issuance and exercise prices pertaining to options outstanding under the plan as of the balance sheet date.

+ References

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-Name Statement of Financial Accounting Standard (FAS)

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The number of exercisable share options (fully vested and expected to vest) that may be converted as of the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

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As of the balance sheet date, the weighted-average exercise price (at which grantees can acquire the shares reserved for issuance) for exercisable stock options that are fully vested or expected to vest.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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