Financial Instruments (Summary Of Activity In Level 3 Financial Instruments) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012	Dec. 31, 2011
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at the beginning of the period	$ 18.6		$ 26.9
Redemption and sales			(7.6)
Change in fair value included in other comprehensive income	(0.1)		(0.8)
Balance at the end of the period	18.5		18.5
Auction Rate Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at the beginning of the period	18.6	25.6	26.9	27.2
Redemption and sales		(0.1)	(7.6)	(0.5)
Change in fair value included in other comprehensive income	0.1	0.4	(0.6)	(0.8)
Balance at the end of the period	18.7	25.9	18.7	25.9
Interest Rate Swap [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at the beginning of the period
Redemption and sales
Change in fair value included in other comprehensive income	(0.2)		(0.2)
Balance at the end of the period	$ (0.2)		$ (0.2)