Financial Instruments (Details) (USD $) In Millions	6 Months Ended
Sep. 30, 2011
Assets
Valuation Technique, Foreign currency exchange derivatives	A
Liabilities
Valuation Technique, Foreign currency exchange derivatives	A
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Money-market funds [Member] \| Recurring [Member]
Assets
Cash equivalents	$ 503.1
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| U.S. Treasury securities [Member] \| Recurring [Member]
Assets
Short-term and long-term investments	50.0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Certificates of deposit [Member] \| Recurring [Member]
Assets
Cash equivalents	61.5
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Auction Rate Securities [Member] \| Recurring [Member]
Assets
Short-term and long-term investments	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Mutual funds [Member] \| Recurring [Member]
Assets
Short-term and long-term investments	17.2
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] \| Recurring [Member]
Assets
Foreign currency forward contracts	0
Total	631.8
Liabilities
Foreign currency forward contracts	0
Total	0
Significant Other Observable Inputs (Level 2) [Member] \| Money-market funds [Member] \| Recurring [Member]
Assets
Cash equivalents	0
Significant Other Observable Inputs (Level 2) [Member] \| U.S. Treasury securities [Member] \| Recurring [Member]
Assets
Short-term and long-term investments	0
Significant Other Observable Inputs (Level 2) [Member] \| Certificates of deposit [Member] \| Recurring [Member]
Assets
Cash equivalents	0
Significant Other Observable Inputs (Level 2) [Member] \| Auction Rate Securities [Member] \| Recurring [Member]
Assets
Short-term and long-term investments	0
Significant Other Observable Inputs (Level 2) [Member] \| Mutual funds [Member] \| Recurring [Member]
Assets
Short-term and long-term investments	0
Significant Other Observable Inputs (Level 2) [Member] \| Recurring [Member]
Assets
Foreign currency forward contracts	11.8
Total	11.8
Liabilities
Foreign currency forward contracts	(8.6)
Total	(8.6)
Significant Unobservable Inputs (Level 3) [Member] \| Money-market funds [Member] \| Recurring [Member]
Assets
Cash equivalents	0
Significant Unobservable Inputs (Level 3) [Member] \| U.S. Treasury securities [Member] \| Recurring [Member]
Assets
Short-term and long-term investments	0
Significant Unobservable Inputs (Level 3) [Member] \| Certificates of deposit [Member] \| Recurring [Member]
Assets
Cash equivalents	0
Significant Unobservable Inputs (Level 3) [Member] \| Auction Rate Securities [Member] \| Recurring [Member]
Assets
Short-term and long-term investments	25.6
Significant Unobservable Inputs (Level 3) [Member] \| Mutual funds [Member] \| Recurring [Member]
Assets
Short-term and long-term investments	0
Significant Unobservable Inputs (Level 3) [Member] \| Recurring [Member]
Assets
Foreign currency forward contracts	0
Total	25.6
Liabilities
Foreign currency forward contracts	0
Total	0
Money-market funds [Member]
Assets
Valuation Technique, Cash equivalents	A
Money-market funds [Member] \| Recurring [Member]
Assets
Cash equivalents	503.1
U.S. Treasury securities [Member]
Assets
Valuation Technique, Short-term and long-term investments	A
U.S. Treasury securities [Member] \| Recurring [Member]
Assets
Short-term and long-term investments	50.0
Certificates of deposit [Member]
Assets
Valuation Technique, Cash equivalents	A
Certificates of deposit [Member] \| Recurring [Member]
Assets
Cash equivalents	61.5
Auction Rate Securities [Member]
Assets
Valuation Technique, Short-term and long-term investments	B
Auction Rate Securities [Member] \| Recurring [Member]
Assets
Short-term and long-term investments	25.6
Mutual funds [Member]
Assets
Valuation Technique, Short-term and long-term investments	A
Mutual funds [Member] \| Recurring [Member]
Assets
Short-term and long-term investments	17.2
Recurring [Member]
Assets
Foreign currency forward contracts	11.8
Total	669.2
Liabilities
Foreign currency forward contracts	(8.6)
Total	$ (8.6)

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