Financial Instruments (Narrative) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended		12 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Mar. 31, 2012
Guarantee by the federal government for bonds issued by public agencies			97.00%		97.00%
Discount rate used in internally developed models, minimum			3.70%
Discount rate used in internally developed models, maximum			4.10%
Discount rate used in internally developed models, weighted average			3.90%
Redemption of available-for-sale holdings by issuers of auction rate securities	$ 0	$ 0.2	$ 7.6	$ 0.4
Unrealized loss on available-for-sale auction rate securities		(0.7)	(0.4)	(0.8)
Foreign currency forward contracts that closed in a gain position	5.5		5.5		8.1
Foreign currency forward contracts that closed in a loss position	4.1		4.1		0.6
Trade finance receivables transferred to financial institutions on a non-recourse basis	39.0	147.8	111.8	159.0
Finance receivables	124.7		124.7
Specific finance receivables fully reserved	0.3		0.3
Senior Unsecured Notes Due 2018 [Member]
Fair value of senior unsecured notes	372.4		372.4		368.4
Carrying value of senior unsecured notes	299.0		299.0		298.9
Senior Unsecured Notes Due 2022 [Member]
Fair value of senior unsecured notes	531.6		531.6		506.6
Carrying value of senior unsecured notes	497.5		497.5		497.4
Foreign Currency Foreign Exchange Contract [Member]
Effect of foreign currency forward contracts	1.9	2.3	4.5	6.0
Net effect of foreign currency forward contracts after including gains and losses on foreign currency exposure	1.0	0.9	0.6	1.9
Auction Rate Securities [Member]
Par value of Auction rate securities held Available-for-sale securities in auction rate securities held			21.7		29.3
Fair value of available-for-sale auction rate securities	18.6		18.6		26.9
Unrealized loss on available-for-sale auction rate securities			$ 3.1