Postretirement benefits (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended						12 Months Ended	3 Months Ended
	Jan. 31, 2012	Jan. 31, 2011	Jan. 31, 2012 Pension Benefit [Member]	Jan. 31, 2011 Pension Benefit [Member]	Jan. 31, 2012 Early Retiree Reinsurance Program [Member]	Jan. 31, 2011 Early Retiree Reinsurance Program [Member]	Oct. 31, 1993 Retiree Supplemental Benefit Trust [Member]	Jan. 31, 2011 Location Fort Wayne [Member] Pension and Other Postretirement Contractual Termination Benefits [Member] Truck [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Benefits Paid			$ 29	$ 21
Defined Benefit Plan, Estimated Future Employer Contributions in Current Fiscal Year			160
Defined Benefit Plan, Contributions by Plan Participants					3	5
Restructuring charges (benefit)	0	22						5
Defined Contribution Plan, Cost Recognized	10	10
Contribution To The Trust Shares							25.5
Profit Sharing Accruals							$ 0