Accumulated Other Comprehensive Income (Loss) (Details) $ in Millions	6 Months Ended
	Jul. 31, 2017 USD ($)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balances - beginning of period	$ (14,232)
Other comprehensive income (loss) before reclassifications	3,088
Amounts reclassified from accumulated other comprehensive income (loss)	44
Balances - end of period	(11,100)
Currency translation and other
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balances - beginning of period	(14,507)
Other comprehensive income (loss) before reclassifications	1,898
Amounts reclassified from accumulated other comprehensive income (loss)	0
Balances - end of period	(12,609)
Unrealized gain on available-for-sale securities
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balances - beginning of period	145
Other comprehensive income (loss) before reclassifications	1,208
Amounts reclassified from accumulated other comprehensive income (loss)	0
Balances - end of period	1,353
Net investment hedges
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balances - beginning of period	1,435
Other comprehensive income (loss) before reclassifications	(149)
Amounts reclassified from accumulated other comprehensive income (loss)	0
Balances - end of period	1,286
Cash flow hedges
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balances - beginning of period	(315)
Other comprehensive income (loss) before reclassifications	128
Amounts reclassified from accumulated other comprehensive income (loss)	15
Balances - end of period	(172)
Minimum pension liability
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balances - beginning of period	(990)
Other comprehensive income (loss) before reclassifications	3
Amounts reclassified from accumulated other comprehensive income (loss)	29
Balances - end of period	$ (958)