Long-term Debt Schedule of Debt (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Apr. 30, 2014	Apr. 30, 2013	Jan. 31, 2014
Debt Instrument [Line Items]
Long-term debt due within one year	$ 3,287	$ 5,967	$ 4,103
Long-term debt	45,699	41,536	41,771
Debt, Long-term and Short-term, Combined Amount	48,986		45,874
Proceeds from Issuance of Debt	4,519
Payments of long-term debt	(1,574)	(1,088)
Reclassifications of Long-Term Debt	(750)
Other	8
Long-Term Debt, Excluding Current Maturities, Other Changes	159
Long-Term Debt, Other Changes	$ 167