Accounting Policies Summary of Significant Accounting Policies (Leases) (Details) - USD ($) $ in Millions |
Apr. 30, 2019 |
Jan. 31, 2019 |
Apr. 30, 2018 |
|---|---|---|---|
| New Accounting Pronouncements or Change in Accounting Principle [Line Items] | |||
| Total assets | $ 234,544 | $ 219,295 | $ 204,927 |
| Operating lease right-of-use assets, net | 16,833 | 0 | 0 |
| Operating lease obligations | 17,467 | ||
| Retained earnings (net of tax) | 76,276 | $ 80,785 | $ 82,982 |
| Accounting Standards Update 2016-02 [Member] | |||
| New Accounting Pronouncements or Change in Accounting Principle [Line Items] | |||
| Total assets | 14,800 | ||
| Total liabilities | 15,100 | ||
| Operating lease right-of-use assets, net | 16,800 | ||
| Operating lease obligations | 17,500 | ||
| Build-to-suit assets derecognized, net | (2,200) | ||
| Build-to-suit liabilities derecognized | (1,700) | ||
| Retained earnings (net of tax) | $ 300 |