Summary of significant accounting policies (Product Warranty Liability) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
	Jan. 31, 2012		Jan. 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		$ 506
Cost accrued and revenues deferred	111		81
Adjustments to pre-existing warranties	123	[1]	9	[1]
Payments and revenues recognized	(106)		(90)
Accrued product warranty and deferred warranty revenue, at end of period	726		506
Accrued product warranty and deferred warranty revenue	726		506
Less: Current portion	324		250
Noncurrent accrued product warranty and deferred warranty revenue	402		256
Adjustments to pre-existing warranties, per diluted share	$ 1.76
Product Warranty Accrual, Preexisting Increase (Decrease), net of tax	81
Product Warranty Accrual, Preexisting Increase Decrease Per Share, Net of Tax	$ 1.16
Extended Warranty Program:
Extended warranty program deferred revenue	282				257
Revenue recognized under extended warranty programs	$ 15		$ 12

[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, or $1.76 per diluted share. Net of tax, the adjustments for changes in estimates amounted to $81 million, or $1.16 per diluted share.