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Retirement and Post-Retirement Benefit Plans - Defined Contribution Plans (Narrative) (Details) - USD ($)
$ in Millions
12 Months Ended
Oct. 31, 2018
Oct. 31, 2017
Oct. 31, 2016
Retirement Benefits [Abstract]      
Total defined contribution expense $ 110 $ 103 $ 100
HP 401(k) Plan      
Defined Contribution Plan Disclosure [Line Items]      
Employer matching contributions, as a percent 100.00%    
Percentage of maximum matching contribution 4.00%