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Short-term Borrowings and Long-term Debt (Schedule of Debt Maturities) (Details) - USD ($)
$ in Millions
Jan. 31, 2019
Jan. 31, 2018
Debt Instrument [Line Items]    
Long-term debt due within one year $ 1,876 $ 3,738
2020 5,347  
2021 3,080  
2022 2,844  
2023 4,595  
Thereafter 27,654  
Long-term debt $ 45,396 $ 33,783