Postretirement benefits (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended	9 Months Ended		12 Months Ended	3 Months Ended				15 Months Ended	12 Months Ended	3 Months Ended
	Jul. 31, 2012	Jul. 31, 2011	Jul. 31, 2012	Jul. 31, 2011	Jul. 31, 2012 Pension Benefit [Member]	Jul. 31, 2011 Pension Benefit [Member]	Jul. 31, 2012 Pension Benefit [Member]	Jul. 31, 2011 Pension Benefit [Member]	Jul. 31, 2012 Other Postretirement Benefit Plans, Defined Benefit [Member]	Jul. 31, 2011 Other Postretirement Benefit Plans, Defined Benefit [Member]	Jul. 31, 2012 Other Postretirement Benefit Plans, Defined Benefit [Member]	Jul. 31, 2011 Other Postretirement Benefit Plans, Defined Benefit [Member]	Jul. 31, 2012 Early Retiree Reinsurance Program [Member]	Jul. 31, 2012 Early Retiree Reinsurance Program [Member]	Jul. 31, 2011 Early Retiree Reinsurance Program [Member]	Oct. 31, 1993 Retiree Supplemental Benefit Trust [Member]	Jul. 31, 2011 Facility Closing [Member] Chatham [Member] Pension Benefit [Member]	Jul. 31, 2011 Facility Closing [Member] Chatham [Member] Other Postretirement Benefit Plans, Defined Benefit [Member]	Jul. 31, 2011 Facility Closing [Member] Chatham [Member] Truck [Member]	Jul. 31, 2011 Facility Closing [Member] Custom Products Operations Union City and Coburg [Member] Truck [Member]	Jul. 31, 2012 Facility Closing [Member] Custom Products Operations Union City and Coburg [Member] Truck [Member]	Apr. 30, 2012 Pension And Other Postretirement Contractual Termination Benefits [Member] Chatham [Member] Truck [Member]	Jul. 31, 2011 Pension And Other Postretirement Contractual Termination Benefits [Member] Custom Products Operations Union City and Coburg [Member] Truck [Member]	Jan. 31, 2011 Pension And Other Postretirement Contractual Termination Benefits [Member] Location Fort Wayne [Member] Truck [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Benefits Paid	$ 30					$ 28	$ 112	$ 80
Defined Benefit Plan, Estimated Future Employer Contributions in Current Fiscal Year					45		45
Defined Benefit Plan, Contributions by Plan Participants													0	3	5
Defined Benefit Plan, Recognized Net Gain (Loss) Due to Curtailments																	8
Defined Benefit Plan, Cost of Providing Special or Contractual Termination Benefits Recognized During Period					0	35	0	38	0	6	(3)	6					35
Postemployment Benefits, Period Expense																		13					4
Defined Contribution Plan, Cost Recognized	8	7	32	25
Contribution To The Trust Shares																25.5
Profit Sharing Accruals																0
Defined Benefit Plan, Contributions by Employer											2	1
Defined Benefit Plan, Estimated Future Employer Contributions in Next Fiscal Year									17		17
Restructuring Charges	$ 4	$ 56	$ 24	$ 80															$ 48	$ 5	$ 10	$ 33		$ 5