Accumulated Other Comprehensive Income (Loss) (Details) $ in Millions	6 Months Ended
	Jul. 31, 2018 USD ($)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balances - beginning of period	$ (10,181)
Adoption of new accounting standard, AOCI	(1,436)
Other comprehensive income (loss) before reclassifications	(1,060)
Amounts reclassified from accumulated other comprehensive income (loss)	(48)
Balances - end of period	(12,629)
Currency translation and other
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balances - beginning of period	(12,136)
Adoption of new accounting standard, AOCI	89
Other comprehensive income (loss) before reclassifications	(1,093)
Amounts reclassified from accumulated other comprehensive income (loss)	0
Balances - end of period	(13,140)
Unrealized gain on available-for-sale securities
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balances - beginning of period	1,646
Adoption of new accounting standard, AOCI	(1,646)
Other comprehensive income (loss) before reclassifications	0
Amounts reclassified from accumulated other comprehensive income (loss)	0
Balances - end of period	0
Net investment hedges
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balances - beginning of period	1,030
Adoption of new accounting standard, AOCI	93
Other comprehensive income (loss) before reclassifications	261
Amounts reclassified from accumulated other comprehensive income (loss)	0
Balances - end of period	1,384
Cash flow hedges
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balances - beginning of period	122
Adoption of new accounting standard, AOCI	28
Other comprehensive income (loss) before reclassifications	(257)
Amounts reclassified from accumulated other comprehensive income (loss)	(25)
Balances - end of period	(82)
Minimum pension liability
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Balances - beginning of period	(843)
Adoption of new accounting standard, AOCI	0
Other comprehensive income (loss) before reclassifications	29
Amounts reclassified from accumulated other comprehensive income (loss)	(23)
Balances - end of period	$ (791)