Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended
	Jul. 31, 2019	Apr. 30, 2019	Jul. 31, 2018	Apr. 30, 2018
Accumulated Other Comprehensive Income Loss [Line Items]
Balances - beginning of period	$ (11,091)	$ (11,542)	$ (10,281)	$ (10,181)
Adoption of new accounting standard, AOCI				(1,436)
Other comprehensive income (loss) before reclassifications	(202)	452	(2,376)	1,316
Amounts reclassified from accumulated other comprehensive income (loss)	23	(1)	28	20
Balances - end of period	(11,270)	(11,091)	(12,629)	(10,281)
Currency Translation and Other
Accumulated Other Comprehensive Income Loss [Line Items]
Balances - beginning of period	(11,612)	(12,085)	(10,745)	(12,136)
Adoption of new accounting standard, AOCI				89
Other comprehensive income (loss) before reclassifications	(165)	496	(2,395)	1,302
Amounts reclassified from accumulated other comprehensive income (loss)	0	(23)	0	0
Balances - end of period	(11,777)	(11,612)	(13,140)	(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	1,503	1,395	1,191	1,030
Adoption of new accounting standard, AOCI				93
Other comprehensive income (loss) before reclassifications	140	108	193	68
Amounts reclassified from accumulated other comprehensive income (loss)	0	0	0	0
Balances - end of period	1,643	1,503	1,384	1,191
Cash Flow Hedges
Accumulated Other Comprehensive Income Loss [Line Items]
Balances - beginning of period	(271)	(140)	73	122
Adoption of new accounting standard, AOCI				28
Other comprehensive income (loss) before reclassifications	(172)	(145)	(171)	(86)
Amounts reclassified from accumulated other comprehensive income (loss)	14	14	16	9
Balances - end of period	(429)	(271)	(82)	73
Minimum Pension Liability
Accumulated Other Comprehensive Income Loss [Line Items]
Balances - beginning of period	(711)	(712)	(800)	(843)
Adoption of new accounting standard, AOCI				0
Other comprehensive income (loss) before reclassifications	(5)	(7)	(3)	32
Amounts reclassified from accumulated other comprehensive income (loss)	9	8	12	11
Balances - end of period	$ (707)	$ (711)	$ (791)	$ (800)