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
	Oct. 31, 2012		Apr. 30, 2012		Jan. 31, 2012		Jul. 31, 2011		Apr. 30, 2011		Jul. 31, 2010		Oct. 31, 2012		Oct. 31, 2011		Oct. 31, 2010
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		$ 492
Cost accrued and revenues deferred													571	[1]	407	[1]	269	[1]
Product Warranty Accrual, Acquisitions															5
Adjustments to pre-existing warranties	149	[1]	104	[1]	123	[1]	30	[1]	27	[1]	25	[1]	404	[2]	79	[2]	51	[2]
Payments and revenues recognized													(455)		(399)		(306)
Accrued product warranty and deferred warranty revenue, at end of period	1,118												1,118		598		506
Less: Current portion	551												551		263		252
Noncurrent accrued product warranty and deferred warranty revenue	567												567		335		254
Product Warranty Accrual, Increase (Decrease)	28	[1]
Product Warranty Accrual, Increase (Decrease), per share	$ 0.41	[1]
Product Warranty Accrual, Preexisting Increase Decrease Per Share, Net of Tax	$ 2.16		$ 1.51		$ 1.76		$ 0.39		$ 0.34		$ 0.34
Truck [Domain]
Extended Warranty Program:
Product Warranty Expense													66
Extended Warranty Programs [Member]
Extended Warranty Program:
Deferred Revenue	364												364		257		167
Revenue recognized under extended warranty programs													63		53		46
Warranty contracts sold in current year [Member] | Truck [Domain]
Extended Warranty Program:
Product Warranty Expense													19
Product Warranty Accrual [Member] | Truck [Domain]
Extended Warranty Program:
Product Warranty Expense													47
Field Campaign to address issues in products sold [Member] | Truck [Domain]
Extended Warranty Program:
Product Warranty Expense													$ 130		$ 23

[1] The warranty estimation for engines sold in 2012 includes a factor for improvements to the design and manufacturing process that was based on historical experience. In the fourth quarter of 2012 we identified a deviation from historic experience and we recorded an adjustment for a change in estimate to increase in the costs accrued for warranty of $28 million, or $0.41 per diluted share for products sold in the first three quarters of 2012.

[2] In the first quarter of 2012, we recorded significant adjustments for changes in estimates of $123 million, or $1.76 per diluted share. In the second quarter of 2012, we recorded significant adjustments for changes in estimates of $104 million, or $1.51 per diluted share. In the fourth quarter of 2012, we recorded significant adjustments for changes in estimates of $149 million, or $2.16 per diluted share. In the third quarter of 2011, we recorded significant adjustments for changes in estimates of $30 million, or $0.39 per diluted share. In the second quarter of 2011, we recorded significant adjustments for changes in estimates of $27 million, or $0.34 per diluted share. In the third quarter of 2010, we recorded significant adjustments for changes in estimates of $25 million, or $0.34 diluted share.