Pension and Other Postretirement Benefits (Changes in Funded Status of Benefit Plans Recognized in Other Comprehensive (Income) Loss) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Apr. 30, 2013	Apr. 30, 2012	Apr. 30, 2011
Pension Benefits [Member]
Amounts recognized in other comprehensive (income) loss
Prior service cost	$ 4	$ 1	$ 0
Actuarial (gain) loss	18	102	(18)
Amortization reclassified to net income:
Prior service cost	(1)	(1)	(1)
Net actuarial loss	(28)	(19)	(18)
Net amount recognized in other comprehensive (income) loss	(7)	83	(37)
Medical and Life Insurance Benefits [Member]
Amounts recognized in other comprehensive (income) loss
Prior service cost	0	0	5
Actuarial (gain) loss	10	4	(10)
Amortization reclassified to net income:
Prior service cost	(1)	0	0
Net actuarial loss	0	0	0
Net amount recognized in other comprehensive (income) loss	$ 9	$ 4	$ (5)

Before tax amount of the benefit improvement costs resulting from a plan amendment that occurred that has not been recognized in net periodic benefit cost.

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-Publisher AICPA

-Name Accounting Research Bulletin (ARB)

-Number 51

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+ Details

- Definition

Before tax amount of the income statement impact of the reclassification adjustment for prior service costs recognized as a component of net period benefit cost.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 130

-Paragraph 17, 19, 24

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

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-URI http://asc.fasb.org/extlink&oid=21915506&loc=d3e1928-114920

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 132R

-Paragraph 5

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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.

Reference 4: http://www.xbrl.org/2003/role/presentationRef

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-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

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-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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Reference 7: http://www.xbrl.org/2003/role/presentationRef

-Publisher AICPA

-Name Accounting Research Bulletin (ARB)

-Number 51

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-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.

Reference 8: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

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-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.

+ Details