Summary of Significant Accounting Policies (Schedule of Property, Plant and Equipment) (Details) - USD ($) $ in Millions	12 Months Ended
	Jan. 31, 2019	Jan. 31, 2018
Property, Plant and Equipment [Line Items]
Property and equipment	$ 185,810	$ 185,154
Accumulated depreciation	(81,493)	(77,479)
Property and equipment, net	104,317	107,675
Land
Property, Plant and Equipment [Line Items]
Property and equipment	24,526	25,298
Buildings and improvements
Property, Plant and Equipment [Line Items]
Property and equipment	$ 101,006	101,155
Buildings and improvements | Minimum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	3 years
Buildings and improvements | Maximum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	40 years
Fixtures and equipment
Property, Plant and Equipment [Line Items]
Property and equipment	$ 54,488	52,695
Fixtures and equipment | Minimum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	1 year
Fixtures and equipment | Maximum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	30 years
Transportation equipment
Property, Plant and Equipment [Line Items]
Property and equipment	$ 2,316	2,387
Transportation equipment | Minimum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	3 years
Transportation equipment | Maximum
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	15 years
Construction in progress
Property, Plant and Equipment [Line Items]
Property and equipment	$ 3,474	$ 3,619