Accumulated Other Comprehensive Income (Loss) (Details) $ in Millions	9 Months Ended
	Oct. 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	3,039
Amounts reclassified from accumulated other comprehensive income (loss)	60
Balances - end of period	(11,133)
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	2,374
Amounts reclassified from accumulated other comprehensive income (loss)	0
Balances - end of period	(12,133)
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	657
Amounts reclassified from accumulated other comprehensive income (loss)	0
Balances - end of period	802
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	(121)
Amounts reclassified from accumulated other comprehensive income (loss)	0
Balances - end of period	1,314
Cash flow hedges
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balances - beginning of period	(315)
Other comprehensive income (loss) before reclassifications	124
Amounts reclassified from accumulated other comprehensive income (loss)	19
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	5
Amounts reclassified from accumulated other comprehensive income (loss)	41
Balances - end of period	$ (944)