Fair Value Measurements (Carrying Value And Fair Value Of Long-Term Debt) (Details) - USD ($) $ in Millions	Jan. 31, 2018	Jan. 31, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	$ 33,783	$ 38,271
Carrying Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	33,783	38,271
Fair Value [Member] | Fair value, inputs, level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, including amounts due within one year, Fair Value	$ 38,766	$ 44,602