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Debt - Short-term Debt (Details) - USD ($)
9 Months Ended
Oct. 31, 2021
Jan. 31, 2021
Debt Instrument [Line Items]    
Maximum borrowing capacity of credit facility $ 3,000,000,000  
Maximum amount outstanding during period 11,000,000  
Commercial paper 0 $ 0
Revolving Credit Facility    
Debt Instrument [Line Items]    
Maximum borrowing capacity of credit facility 3,000,000,000  
Revolving Credit Facility | 5-year Back-up Credit Facility    
Debt Instrument [Line Items]    
Maximum borrowing capacity of credit facility $ 1,000,000,000  
Expiration period 364 days  
Revolving Credit Facility | Five year back up credit facility expiring December 2020    
Debt Instrument [Line Items]    
Maximum borrowing capacity of credit facility $ 2,000,000,000  
Expiration period 5 years