Financial Instruments (Input Levels And Valuation Techniques For Determination Of Fair Values Of Financial Instruments) (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Mar. 31, 2012
Liabilities
Interest rate swap	$ 0.2
Recurring [Member]
Assets
Total	375.2	966.0
Liabilities
Total	2.5	0.6
Recurring [Member] | Valuation Technique A [Member]
Assets
Foreign currency forward contracts	3.8	8.1
Liabilities
Foreign currency forward contracts	2.3	0.6
Recurring [Member] | Valuation Technique B [Member]
Liabilities
Interest rate swap	0.2
Recurring [Member] | Money-Market Funds [Member] | Valuation Technique A [Member]
Assets
Cash equivalents	26.2	769.3
Recurring [Member] | United States Treasury Securities [Member] | Valuation Technique A [Member]
Assets
Cash equivalents	150.0	49.9
Short-term and long-term investments	128.7	92.2
Recurring [Member] | Auction Rate Securities [Member] | Valuation Technique B [Member]
Assets
Short-term and long-term investments	18.7	26.9
Recurring [Member] | United States Government Agency Bonds [Member] | Valuation Technique A [Member]
Assets
Short-term and long-term investments	15.4
Recurring [Member] | Corporate Bonds And Commercial Paper [Member] | Valuation Technique A [Member]
Assets
Short-term and long-term investments	12.0
Recurring [Member] | Mutual Funds [Member] | Valuation Technique A [Member]
Assets
Short-term and long-term investments	20.4	19.6
Recurring [Member] | Level 1 [Member]
Assets
Total	325.3	931.0
Recurring [Member] | Level 1 [Member] | Money-Market Funds [Member] | Valuation Technique A [Member]
Assets
Cash equivalents	26.2	769.3
Recurring [Member] | Level 1 [Member] | United States Treasury Securities [Member] | Valuation Technique A [Member]
Assets
Cash equivalents	150.0	49.9
Short-term and long-term investments	128.7	92.2
Recurring [Member] | Level 1 [Member] | Mutual Funds [Member] | Valuation Technique A [Member]
Assets
Short-term and long-term investments	20.4	19.6
Recurring [Member] | Level 2 [Member]
Assets
Total	31.2	8.1
Liabilities
Total	2.3	0.6
Recurring [Member] | Level 2 [Member] | Valuation Technique A [Member]
Assets
Foreign currency forward contracts	3.8	8.1
Liabilities
Foreign currency forward contracts	2.3	0.6
Recurring [Member] | Level 2 [Member] | United States Government Agency Bonds [Member] | Valuation Technique A [Member]
Assets
Short-term and long-term investments	15.4
Recurring [Member] | Level 2 [Member] | Corporate Bonds And Commercial Paper [Member] | Valuation Technique A [Member]
Assets
Short-term and long-term investments	12.0
Recurring [Member] | Level 3 [Member]
Assets
Total	18.7	26.9
Liabilities
Total	0.2
Recurring [Member] | Level 3 [Member] | Valuation Technique B [Member]
Liabilities
Interest rate swap	0.2
Recurring [Member] | Level 3 [Member] | Auction Rate Securities [Member] | Valuation Technique B [Member]
Assets
Short-term and long-term investments	$ 18.7	$ 26.9