Statements of Stockholder's Equity (Parenthetical) (USD $) In Millions, except Per Share data	12 Months Ended
Apr. 30, 2011	Apr. 30, 2010	Apr. 30, 2009
Retained Earnings
Cash dividends	$ 2.24	$ 1.18	$ 1.12
Change in measurement date of postretirement benefit plans, tax			$ 2
Accumulated Other Comprehensive Income (Loss)
Change in measurement date of postretirement benefit plans, tax			$ (6)

Tax effect of adjustment increasing or decreasing accumulated other comprehensive income due to a change in the measurement date for a defined benefit pension and other postretirement plan in the initial application of the measurement provisions of FAS 158.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 158
-Paragraph 21
-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant