Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended
	Apr. 30, 2019	Apr. 30, 2018
Accumulated Other Comprehensive Income Loss [Line Items]
Balances - beginning of period	$ (11,542)	$ (10,181)
Adoption of new accounting standard, AOCI		(1,436)
Other comprehensive income (loss) before reclassifications	452	1,316
Amounts reclassified from accumulated other comprehensive income (loss)	(1)	20
Balances - end of period	(11,091)	(10,281)
Currency Translation and Other
Accumulated Other Comprehensive Income Loss [Line Items]
Balances - beginning of period	(12,085)	(12,136)
Adoption of new accounting standard, AOCI		89
Other comprehensive income (loss) before reclassifications	496	1,302
Amounts reclassified from accumulated other comprehensive income (loss)	(23)	0
Balances - end of period	(11,612)	(10,745)
Unrealized Gain on Available-for-Sale Securities
Accumulated Other Comprehensive Income Loss [Line Items]
Balances - beginning of period	0	1,646
Adoption of new accounting standard, AOCI		(1,646)
Other comprehensive income (loss) before reclassifications	0	0
Amounts reclassified from accumulated other comprehensive income (loss)	0	0
Balances - end of period	0	0
Net Investment Hedges
Accumulated Other Comprehensive Income Loss [Line Items]
Balances - beginning of period	1,395	1,030
Adoption of new accounting standard, AOCI		93
Other comprehensive income (loss) before reclassifications	108	68
Amounts reclassified from accumulated other comprehensive income (loss)	0	0
Balances - end of period	1,503	1,191
Cash Flow Hedges
Accumulated Other Comprehensive Income Loss [Line Items]
Balances - beginning of period	(140)	122
Adoption of new accounting standard, AOCI		28
Other comprehensive income (loss) before reclassifications	(145)	(86)
Amounts reclassified from accumulated other comprehensive income (loss)	14	9
Balances - end of period	(271)	73
Minimum Pension Liability
Accumulated Other Comprehensive Income Loss [Line Items]
Balances - beginning of period	(712)	(843)
Adoption of new accounting standard, AOCI		0
Other comprehensive income (loss) before reclassifications	(7)	32
Amounts reclassified from accumulated other comprehensive income (loss)	8	11
Balances - end of period	$ (711)	$ (800)