Schedule of Debt (Details) - USD ($) $ in Millions	6 Months Ended
	Jul. 31, 2015	Jul. 31, 2014	Jan. 31, 2015
Debt Instrument [Line Items]
Long-term debt due within one year	$ 4,024	$ 4,639	$ 4,791
Long-term debt	38,581	42,801	40,889
Debt, Long-term and Short-term, Combined Amount	42,605		$ 45,680
Proceeds from issuance of long-term debt	42	4,565
Payments of long-term debt	(3,159)	$ (2,868)
Amounts reclassified from long-term debt	(2,000)
Amounts reclassified to short-term debt	2,000
Long-Term Debt, Current Maturities, Other Changes	392
Long-Term Debt, Excluding Current Maturities, Other Changes	(350)
Long-Term Debt, Other Changes	42
Unsecured Debt
Debt Instrument [Line Items]
Payments of long-term debt	$ (2,980)