Summary of Significant Accounting Policies (Schedule of Property, Plant and Equipment) (Details) - USD ($) $ in Millions	12 Months Ended
	Jan. 31, 2018	Jan. 31, 2017
Property, Plant and Equipment [Line Items]
Property and equipment	$ 185,154	$ 179,492
Accumulated depreciation	(77,479)	(71,782)
Property and equipment, net	107,675	107,710
Land
Property, Plant and Equipment [Line Items]
Property and equipment	25,298	24,801
Buildings and improvements
Property, Plant and Equipment [Line Items]
Property and equipment	$ 101,155	98,547
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	$ 52,695	48,998
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	$ 2,387	2,845
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	$ 3,619	$ 4,301