Taxes (Schedule of income tax provision) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Jan. 31, 2015	Jan. 31, 2014	Jan. 31, 2013
Taxes [Abstract]
U.S. federal	$ 6,165us-gaap_CurrentFederalTaxExpenseBenefit	$ 6,377us-gaap_CurrentFederalTaxExpenseBenefit	$ 5,611us-gaap_CurrentFederalTaxExpenseBenefit
U.S. state and local	810	719	622
International	1,529us-gaap_CurrentForeignTaxExpenseBenefit	1,523us-gaap_CurrentForeignTaxExpenseBenefit	1,743us-gaap_CurrentForeignTaxExpenseBenefit
Total current tax provision	8,504us-gaap_CurrentIncomeTaxExpenseBenefit	8,619us-gaap_CurrentIncomeTaxExpenseBenefit	7,976us-gaap_CurrentIncomeTaxExpenseBenefit
U.S. federal	(387)	(72)	38
U.S. state and local	(55)	37	(8)
International	(77)	(479)	(48)
Total deferred tax expense (benefit)	(519)us-gaap_DeferredIncomeTaxExpenseBenefit	(514)us-gaap_DeferredIncomeTaxExpenseBenefit	(18)us-gaap_DeferredIncomeTaxExpenseBenefit
Total provision for income taxes	$ 7,985us-gaap_IncomeTaxExpenseBenefit	$ 8,105us-gaap_IncomeTaxExpenseBenefit	$ 7,958us-gaap_IncomeTaxExpenseBenefit

Amount of current federal tax expense (benefit) pertaining to income (loss) from continuing operations.

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