Financial Instruments (Input Levels And Valuation Techniques For Determination Of Fair Values Of Financial Instruments) (Detail) (USD $) In Millions, unless otherwise specified	6 Months Ended
Sep. 30, 2012
Recurring [Member]
Assets
Foreign currency forward contracts	5.5
Total	562.0
Liabilities
Foreign currency forward contracts	4.1
Total	4.1
Quoted Prices In Active Markets For Identical Assets (Level 1) [Member] \| Recurring [Member]
Assets
Total	537.9
Significant Other Observable Inputs (Level 2) [Member] \| Recurring [Member]
Assets
Foreign currency forward contracts	5.5
Total	5.5
Liabilities
Foreign currency forward contracts	4.1
Total	4.1
Significant Unobservable Inputs (Level 3) [Member] \| Recurring [Member]
Assets
Total	18.6
Money-Market Funds [Member]
Liabilities
Valuation Technique	A
Money-Market Funds [Member] \| Recurring [Member]
Assets
Cash equivalents	182.4
Money-Market Funds [Member] \| Quoted Prices In Active Markets For Identical Assets (Level 1) [Member] \| Recurring [Member]
Assets
Cash equivalents	182.4
United States Treasury Securities [Member]
Liabilities
Valuation Technique	A
United States Treasury Securities [Member] \| Recurring [Member]
Assets
Cash equivalents	200.0
Short-term and long-term investments	134.8
United States Treasury Securities [Member] \| Quoted Prices In Active Markets For Identical Assets (Level 1) [Member] \| Recurring [Member]
Assets
Cash equivalents	200.0
Short-term and long-term investments	134.8
Auction Rate Securities [Member]
Liabilities
Valuation Technique	B
Auction Rate Securities [Member] \| Recurring [Member]
Assets
Short-term and long-term investments	18.6
Auction Rate Securities [Member] \| Significant Unobservable Inputs (Level 3) [Member] \| Recurring [Member]
Assets
Short-term and long-term investments	18.6
Mutual Funds [Member]
Liabilities
Valuation Technique	A
Mutual Funds [Member] \| Recurring [Member]
Assets
Short-term and long-term investments	20.7
Mutual Funds [Member] \| Quoted Prices In Active Markets For Identical Assets (Level 1) [Member] \| Recurring [Member]
Assets
Short-term and long-term investments	20.7
Foreign Currency Forward Contracts [Member]
Liabilities
Valuation Technique	A

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item includes currency on hand as well as demand deposits with banks or financial institutions. It also includes other kinds of accounts that have the general characteristics of demand deposits in that the Company may deposit additional funds at any time and also effectively may withdraw funds at any time without prior notice or penalty. Cash equivalents, excluding items classified as marketable securities, include short-term, highly liquid investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three years ago does not become a cash equivalent when its remaining maturity is three months.

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Fair values as of the balance sheet date of all assets resulting from contracts that meet the criteria of being accounted for as derivative instruments, net of the effects of master netting arrangements.

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- Definition

Derivative instrument obligations meeting the definition of a liability which the Company is a party to as of the balance sheet date.

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- Definition

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