Schedule of Debt (Details) - USD ($) $ in Millions	9 Months Ended
	Oct. 31, 2015	Oct. 31, 2014	Jan. 31, 2015
Debt Instrument [Line Items]
Long-term debt due within one year	$ 2,746	$ 4,854	$ 4,791
Long-term debt	38,617	41,519	40,889
Total	41,363		$ 45,680
Proceeds from issuance of long-term debt	41	5,120
Repayments of long-term debt	(4,422)	$ (3,883)
Reclassifications of long-term debt	(2,000)
Reclassifications of long-term debt	2,000
Long-term debt, current maturities, other changes	377
Long-term debt, excluding current maturities, other changes	(313)
Long-term debt, other changes	64
Unsecured debt
Debt Instrument [Line Items]
Repayments of long-term debt	$ (4,230)