Financial Instruments (Details) (USD $) In Millions	3 Months Ended
	Jun. 30, 2011
Assets
Foreign currency forward contracts	$ 1.5
Total	962.1
Valuation Technique, Foreign currency exchange derivatives	A
Liabilities
Foreign currency forward contracts	(2.7)
Total	(2.7)
Valuation Technique, Foreign currency exchange derivatives	A
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Assets
Foreign currency forward contracts	0
Total	933.8
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Money-market funds [Member]
Assets
Cash equivalents	783.1
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | U.S. Treasury securities [Member]
Assets
Short-term and long-term investments	49.9
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Certificates of deposit [Member]
Assets
Cash equivalents	81.5
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Auction Rate Securities [Member]
Assets
Short-term and long-term investments	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Mutual funds [Member]
Assets
Short-term and long-term investments	19.3
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Liabilities
Foreign currency forward contracts	0
Total	0
Significant Other Observable Inputs (Level 2) [Member]
Assets
Foreign currency forward contracts	1.5
Total	1.5
Significant Other Observable Inputs (Level 2) [Member] | Money-market funds [Member]
Assets
Cash equivalents	0
Significant Other Observable Inputs (Level 2) [Member] | U.S. Treasury securities [Member]
Assets
Short-term and long-term investments	0
Significant Other Observable Inputs (Level 2) [Member] | Certificates of deposit [Member]
Assets
Cash equivalents	0
Significant Other Observable Inputs (Level 2) [Member] | Auction Rate Securities [Member]
Assets
Short-term and long-term investments	0
Significant Other Observable Inputs (Level 2) [Member] | Mutual funds [Member]
Assets
Short-term and long-term investments	0
Significant Other Observable Inputs (Level 2) [Member]
Liabilities
Foreign currency forward contracts	(2.7)
Total	(2.7)
Significant Unobservable Inputs (Level 3) [Member]
Assets
Foreign currency forward contracts	0
Total	26.8
Significant Unobservable Inputs (Level 3) [Member] | Money-market funds [Member]
Assets
Cash equivalents	0
Significant Unobservable Inputs (Level 3) [Member] | U.S. Treasury securities [Member]
Assets
Short-term and long-term investments	0
Significant Unobservable Inputs (Level 3) [Member] | Certificates of deposit [Member]
Assets
Cash equivalents	0
Significant Unobservable Inputs (Level 3) [Member] | Auction Rate Securities [Member]
Assets
Short-term and long-term investments	26.8
Significant Unobservable Inputs (Level 3) [Member] | Mutual funds [Member]
Assets
Short-term and long-term investments	0
Significant Unobservable Inputs (Level 3) [Member]
Liabilities
Foreign currency forward contracts	0
Total	0
Money-market funds [Member]
Assets
Cash equivalents	783.1
Valuation Technique, Cash equivalents	A
U.S. Treasury securities [Member]
Assets
Short-term and long-term investments	49.9
Valuation Technique, Short-term and long-term investments	A
Certificates of deposit [Member]
Assets
Cash equivalents	81.5
Valuation Technique, Cash equivalents	A
Auction Rate Securities [Member]
Assets
Short-term and long-term investments	26.8
Valuation Technique, Short-term and long-term investments	B
Mutual funds [Member]
Assets
Short-term and long-term investments	$ 19.3
Valuation Technique, Short-term and long-term investments	A