Summary of significant accounting policies (Product Warranty Liability) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended						9 Months Ended
	Jul. 31, 2012	Apr. 30, 2012		Jan. 31, 2012		Jul. 31, 2011	Jul. 31, 2012	Jul. 31, 2011	Oct. 31, 2011
Accrued Product Warranty And Deferred Warranty Revenue, Standard And Extended Warranty Programs, Roll Forward:
Accrued product warranty and deferred warranty revenue, at beginning of period				$ 598			$ 598	$ 506
Cost accrued and revenues deferred							353	281
Adjustments to pre-existing warranties	10	104	[1]	123	[1]		255	66
Payments and revenues recognized							(324)	(288)
Accrued product warranty and deferred warranty revenue, at end of period	882					565	882	565
Less: Current portion	448					254	448	254
Noncurrent accrued product warranty and deferred warranty revenue	434					311	434	311
Product Warranty Accrual, Preexisting Increase (Decrease), net of tax		63		75
Product Warranty Accrual, Preexisting Increase Decrease Per Share, Net of Tax		$ 0.92		$ 1.07
Extended Product Warranty Accrual	332						332		257
Extended Warranty Program:
Revenue recognized under extended warranty programs	17					13	48	39
Revenue extended warranty service contracts							$ 24

[1] Adjustments to pre-existing warranties reflect changes in our estimate of warranty costs for products sold in prior periods. Such adjustments typically occur when claims experience deviates from historic and expected trends. Our warranty liability is generally affected by component failure rates, repair costs, and the timing of failures. Future events and circumstances related to these factors could materially change our estimates and require adjustments to our liability. In addition, new product launches require a greater use of judgment in developing estimates until historical experience becomes available. In the first quarter of 2012, we recorded adjustments for changes in estimates of $123 million ($75 million, or $1.07 per diluted share, net of tax). In the second quarter of 2012, we recorded adjustments for changes in estimates of $104 million ($63 million, or $0.92 per diluted share, net of tax).