Fair Value Measurements (Carrying Value And Fair Value Of Long-Term Debt) (Details) - USD ($) $ in Millions |
Apr. 30, 2019 |
Jan. 31, 2019 |
|---|---|---|
| Carrying value | ||
| Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | ||
| Long-term debt | $ 48,889 | $ 45,396 |
| Fair value | Inputs, Level 2 [Member] | ||
| Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | ||
| Long-term debt, including amounts due within one year, fair value | $ 53,707 | $ 49,570 |