Contingencies (Details) $ in Millions	3 Months Ended
	Jul. 31, 2019 USD ($)	Jan. 31, 2019 USD ($)
Asda Equal Value Lawsuit [Domain]
Loss Contingencies [Line Items]
Loss Contingency, Pending Claims, Number	30,000
Foreign Corrupt Practices Act [Member]
Loss Contingencies [Line Items]
Loss Contingency, Estimate of Possible Loss		$ 283
Litigation Settlement, Amount Awarded to Other Party	$ 283
Department of Justice [Member] | Foreign Corrupt Practices Act [Member]
Loss Contingencies [Line Items]
Litigation Settlement, Amount Awarded to Other Party	138
Department of Justice [Member] | WMT Brasilia S.a.r.l. [Member] | Foreign Corrupt Practices Act [Member]
Loss Contingencies [Line Items]
Litigation Settlement, Amount Awarded to Other Party	4
Securities and Exchange Commission [Member] | Foreign Corrupt Practices Act [Member]
Loss Contingencies [Line Items]
Litigation Settlement, Amount Awarded to Other Party	$ 145