Summary of Significant Accounting Policies - Product Warranty Liability (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended						12 Months Ended						3 Months Ended
	Oct. 31, 2014	Jul. 31, 2014	Oct. 31, 2013	Apr. 30, 2013	Jan. 31, 2013	Jul. 31, 2012	Oct. 31, 2014		Oct. 31, 2013		Oct. 31, 2012		Apr. 30, 2014	Jan. 31, 2014	Jul. 31, 2013	Oct. 31, 2012	Apr. 30, 2012	Jan. 31, 2012
Accrued Product Warranty And Deferred Warranty Revenue, Standard And Extended Warranty Programs, Roll Forward:
Balance at beginning of period					$ 1,118		$ 1,349		$ 1,118		$ 598			$ 1,349				$ 598
Costs accrued and revenues deferred							302		469		575
Product Warranty Accrual, Divestures							0		(3)		0
Currency translation adjustment							(4)		(2)		(4)
Adjustments to pre-existing warranties(A)(B)	(10)	(29)	152			10	55	[1],[2]	404	[1],[2]	404	[1],[2]
Payments and revenues recognized							(505)		(637)		(455)
Balance at end of period	1,197		1,349				1,197		1,349		1,118					1,118
Less: Current portion	535		601				535		601		551					551
Noncurrent accrued product warranty and deferred warranty revenue	662		748				662		748		567					567
Warranty Recoveries				13	27
Extended Warranty Programs [Member]
Extended Warranty Program:
Deferred Revenue, Revenue Recognized							132		87		63
Deferred Revenue	437		420				437		420		364					364
recoverable [Member]
Accrued Product Warranty And Deferred Warranty Revenue, Standard And Extended Warranty Programs, Roll Forward:
Adjustments to pre-existing warranties(A)(B)					13
Product Warranty Accrual [Member]
Accrued Product Warranty And Deferred Warranty Revenue, Standard And Extended Warranty Programs, Roll Forward:
Adjustments to pre-existing warranties(A)(B)	$ 25	$ 30		$ 164	$ 40								$ 42	$ 52	$ 48	$ 149	$ 104	$ 123
Product Warranty Accrual, Preexisting Increase Decrease Per Share, Net of Tax		$ (0.36)	$ 1.89	$ 2.04	$ 0.50								$ 0.52	$ 0.64	$ 0.60	$ 2.16	$ 1.51	$ 1.76

[1] (B)In the first quarter of 2013, we recognized $13 million of charges for adjustments to pre-existing warranties for a specific warranty issue related to component parts from a supplier. Also during the first quarter of 2013, we reached an agreement for reimbursement from this supplier for this amount and other costs previously accrued. As a result of this agreement, we recognized a recovery of $27 million within Costs of products sold and recorded a receivable within Other current assets. In the second quarter of 2013, we recognized a warranty recovery of $13 million within Income (loss) from discontinued operations, net of tax and recorded a receivable within Other current assets.In the third quarter of 2012, we recognized $10 million of adjustments to pre-existing warranties for a specific warranty issue related to component parts from a supplier. Also during the quarter, we reached agreement for reimbursement from such supplier and recognized a recovery for that amount and recorded a receivable within Other current assets.

[2] (A)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 2014, we recorded adjustments for changes in estimates of $52 million or $0.64 per diluted share. In the second quarter of 2014, we recorded adjustments for changes in estimates of $42 million, or $0.52 per diluted share. In the third quarter of 2014, we recognized a benefit for adjustments to pre-existing warranties of $(29) million, or $(0.36) per diluted share. Included in the 2014 adjustments is a $36 million correction of prior-period errors, primarily related to pre-existing warranties. For more information on the errors identified, see 2014 Out-of-Period Adjustments. The impact of income taxes on the 2014 adjustments is not material due to our deferred tax valuation allowances on our U.S. deferred tax assets.In the first quarter of 2013, we recorded adjustments for changes in estimates of $40 million or $0.50 per diluted share. In the second quarter of 2013, we recorded adjustments for changes in estimates of $164 million, or $2.04 per diluted share. In the third quarter of 2013, we recorded adjustments for changes in estimates of $48 million, or $0.60 per diluted share. In the fourth quarter of 2013, we recorded adjustments for changes in estimates of $152 million, or $1.89 per diluted share. The impact of income taxes on the 2013 adjustments is not material due to our deferred tax valuation allowances on our U.S. deferred tax assets. In the first quarter of 2012, we recorded adjustments for changes in estimates of $123 million, or $1.76 per diluted share. In the second quarter of 2012, we recorded adjustments for changes in estimates of $104 million, or $1.51 per diluted share. In the fourth quarter of 2012, we recorded adjustments for changes in estimates of $149 million, or $2.16 per diluted share.