Accumulated Other Comprehensive Income (Loss) (Details) $ in Millions	3 Months Ended
	Apr. 30, 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	1,316
Amounts reclassified from accumulated other comprehensive income (loss)	(20)
Balances - end of period	(10,281)
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	1,302
Amounts reclassified from accumulated other comprehensive income (loss)	0
Balances - end of period	(10,745)
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	68
Amounts reclassified from accumulated other comprehensive income (loss)	0
Balances - end of period	1,191
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	(86)
Amounts reclassified from accumulated other comprehensive income (loss)	(9)
Balances - end of period	73
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	32
Amounts reclassified from accumulated other comprehensive income (loss)	(11)
Balances - end of period	$ (800)