Summary of significant accounting policies (Product Warranty Liability) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended					6 Months Ended
	Apr. 30, 2012		Jan. 31, 2012		Apr. 30, 2011	Apr. 30, 2012	Apr. 30, 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						236	175
Adjustments to pre-existing warranties						227	36
Payments and revenues recognized						(217)	(187)
Accrued product warranty and deferred warranty revenue, at end of period	844				530	844	530
Less: Current portion	365				240	365	240
Noncurrent accrued product warranty and deferred warranty revenue	479				290	479	290
Adjustment for Changes in Estimate to Preexisting Warranty	104	[1]	123	[1]			27
Product Warranty Accrual, Preexisting Increase (Decrease), net of tax	100		119			24
Product Warranty Accrual, Preexisting Increase Decrease Per Share, Net of Tax	$ 1.46		$ 1.7			$ 0.31
Extended Warranty Program:
Extended warranty program deferred revenue	308					308		257
Revenue recognized under extended warranty programs	16				13	31	25
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, $119 million net of tax, or $1.70 per diluted share. In the second quarter of 2012, we recorded adjustments for changes in estimates of $104 million, $100 million net of tax, or $1.46 per diluted share. In the second quarter of 2011, we recorded adjustments for changes in estimates of $27 million, $24 million net of tax, or $0.31 per diluted share.