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Debt - Narrative (Details)
Oct. 31, 2020
USD ($)
Jan. 31, 2020
USD ($)
Apr. 30, 2018
USD ($)
Line of Credit Facility [Line Items]      
Outstanding borrowings $ 2,676,000,000 $ 2,677,000,000  
Closing trading price      
Line of Credit Facility [Line Items]      
Long-term debt measurement input 100    
Revolving Credit Facility      
Line of Credit Facility [Line Items]      
Maximum borrowing capacity     $ 1,000,000,000.0
Outstanding borrowings $ 0    
Senior Notes | Significant Other Observable Inputs (Level 2)      
Line of Credit Facility [Line Items]      
Senior Notes fair value $ 2,800,000,000 $ 2,700,000,000