Supplementary Financial Information - Value of Remaining Performance Obligations (Details) $ in Billions	Jul. 31, 2020 USD ($)
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Remaining performance obligations	$ 4.2
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-08-01
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Remaining performance obligations	$ 1.8
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligations period	12 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-08-01
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Remaining performance obligations	$ 2.4
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligations period