Income Taxes (Reconciliation Of Income Tax Computed At United States Federal Statutory Rate To Reported Income Tax Expense) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2011
Income Tax Disclosure [Abstract]
Expense computed at United States statutory rate, amount	$ 149.8	$ 185.5	$ 186.0
Effect of foreign rate differentials, amount	(44.1)	(40.6)	(54.6)
Extraterritorial income and production activities deductions, amount	(24.7)	(25.7)	(24.7)
State income taxes, net of federal benefit, amount	7.6	6.8	8.7
Settlements with tax authorities, amount		(6.2)	(57.2)
Other, net, amount	8.3	9.2	16.9
Income tax provision	$ 96.9	$ 129.0	$ 75.1
Expense computed at United States statutory rate, percentage	35.00%	35.00%	35.00%
Effect of foreign rate differentials, percentage	(10.30%)	(7.70%)	(10.30%)
Extraterritorial income and production activities deductions, percentage	(5.80%)	(4.80%)	(4.60%)
State income taxes, net of federal benefit, percentage	1.80%	1.30%	1.60%
Settlements with tax authorities, percentage		(1.20%)	(10.80%)
Other, net, percentage	1.90%	1.70%	3.20%
Income tax provision, percentage	22.60%	24.30%	14.10%