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Summary of Significant Accounting Policies - Product Warranty Liability (Details) - USD ($)
$ in Millions
6 Months Ended 12 Months Ended
Apr. 30, 2020
Apr. 30, 2019
Oct. 31, 2019
Oct. 31, 2018
Product Liability Contingency [Line Items]        
Standard and Extended Product Warranty Accrual $ 468 $ 523 $ 510 $ 529
Product Warranty Accrual, Warranties Issued 73 118    
Accrued Product Warranty And Deferred Warranty Revenue, Standard And Extended Warranty Programs, Roll Forward:        
Adjustments to pre-existing warranties 17 2    
Extended Warranty Program:        
Product Warranty Accrual, Payments (132) (138)    
standard and extended product warranty other adjustments 0 12    
Product Warranty Accrual, Current 215 261    
Product Warranty Accrual, Noncurrent $ 253 $ 262    
increase in deferred revenue due to adoption of 606 [Domain]        
Extended Warranty Program:        
standard and extended product warranty other adjustments     14  
Reduction In Liability        
Extended Warranty Program:        
standard and extended product warranty other adjustments     $ 2