Income Taxes (Details 1) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Mar. 31, 2012 Rate	Mar. 31, 2011 Rate	Mar. 31, 2010 Rate
Reconciliation of income tax computed at united states federal statutory rate to reported tax expense
Expense computed at United States statutory rate, amount	$ 185.5	$ 186.0	$ 176.5
Expense computed at United States statutory rate, percentage	35.00%	35.00%	35.00%
Effect of foreign rate differentials, amount	(40.6)	(54.6)	(29.7)
Effect of foreign rate differentials, percentage	(7.70%)	(10.30%)	(5.90%)
Extraterritorial income and production activities deductions, amount	(25.7)	(24.7)	(21.5)
Extraterritorial income and production activities deductions, percentage	(4.80%)	(4.60%)	(4.30%)
State income taxes, net of federal benefit, amount	6.8	8.7	3.1
State income taxes, net of federal benefit, percentage	1.30%	1.60%	0.60%
Settlements with tax authorities, amount	(6.2)	(57.2)	(30.0)
Settlements with tax authorities, percentage	(1.20%)	(10.80%)	(5.90%)
Other, net, amount	9.2	16.9	(0.3)
Other, net, percentage	1.70%	3.20%	0.00%
Income tax provision	$ 129.0	$ 75.1	$ 98.1
Income tax provision, percentage	24.30%	14.10%	19.50%