Long-term Debt Schedule of Debt (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Oct. 31, 2014	Oct. 31, 2013	Jan. 31, 2014
Debt Instrument [Line Items]
Long-term debt due within one year	$ 4,874	$ 4,147	$ 4,103
Long-term debt	41,720	41,702	41,771
Debt, Long-term and Short-term, Combined Amount	46,594		45,874
Proceeds from issuance of long-term debt	5,120	7,053
Payments of long-term debt	(3,883)	(4,943)
Reclassified from Long-Term Debt	4,324
Reclassifications of Long-Term Debt	(4,324)
Other	330
Long-Term Debt, Excluding Current Maturities, Other Changes	(847)
Long-Term Debt, Other Changes	$ (517)