Statements of Consolidated Shareholders' Equity (Parenthetical) (USD $)	3 Months Ended	12 Months Ended
Jul. 31, 2011	Jul. 31, 2010	Apr. 30, 2011	Apr. 30, 2010	Apr. 30, 2009
Statement of Consolidated Shareholders' Equity [Abstract]
Dividend declared per common share	$ 0.48	$ 0.40	$ 1.68	$ 1.45	$ 6.31

Aggregate dividends declared during the period for each share of common stock outstanding.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Article 3

Name:	us-gaap_CommonStockDividendsPerShareDeclared
Namespace Prefix:	us-gaap
Data Type:	us-types:perShareItemType
Balance Type:	na
Period Type:	duration