Commitments and Contingencies - Environmental Matter (Details) (USD $)	3 Months Ended
	Jul. 31, 2014
EPA's FFS remediation approaches [Member] | Minimum [Member]
Environmental Matter Disclosure [Line Items]
Estimated Remediation Costs Low Estimate	$ 360,000,000
EPA's FFS remediation approaches [Member] | Maximum [Member]
Environmental Matter Disclosure [Line Items]
Estimated Remediation Costs High Estimate	3,250,000,000
EPA-recommended remediation approach [Member] | Minimum [Member]
Environmental Matter Disclosure [Line Items]
Estimated Remediation Costs EPA Preferred Method Low Estimate	950,000,000
EPA-recommended remediation approach [Member] | Maximum [Member]
Environmental Matter Disclosure [Line Items]
Estimated Remediation Costs EPA Preferred Method High Estimate	$ 1,731,000,000