Short-term Borrowings and Long-term Debt Schedule of Long-term Debt Instruments (Details) - USD ($) $ in Millions	6 Months Ended
	Jul. 31, 2019	Jul. 31, 2018	Jan. 31, 2019
Short-term Borrowings and Long-term Debt [Abstract]
Long-term Debt, Current Maturities	$ 4,396	$ 1,090	$ 1,876
Long-term Debt, Excluding Current Maturities	44,404	44,958	43,520
Debt, Long-term and Short-term, Combined Amount	48,800		$ 45,396
Proceeds from issuance of long-term debt, current maturities	0
Proceeds from Issuance of Long-term Debt	4,020	$ 15,851
Repayments of Long-term Debt, Book Value, Current Maturities	(407)
Repayments of Long-term Debt, Excluding Current Maturities, Book Value	0
Repayments of Long-term Debt, Total, Book Value	(407)
Reclassifications of long-term debt (to debt due within one year)	2,932
Reclassifications of long-term debt (out of long-term debt)	(2,932)
Amounts Reclassified to Short-term Debt, Total	0
Long-Term Debt, Current Maturities, Other Changes	(5)
Long-Term Debt, Excluding Current Maturities, Other Changes	(204)
Long-Term Debt, Other Changes	$ (209)