Accounting Policies Summary of Significant Accounting Policies (Details) - USD ($) |
Apr. 30, 2019 |
Jan. 31, 2019 |
Apr. 30, 2018 |
Jan. 31, 2018 |
|---|---|---|---|---|
| Restricted Cash [Abstract] | ||||
| Restricted Cash | $ 37,000,000 | $ 34,000,000 | $ 300,000,000 | $ 300,000,000 |
| Revenue from Contract with Customer [Abstract] | ||||
| Receivables from transactions with customers, net | 2,566,000,000 | 2,538,000,000 | ||
| Deferred gift card revenue | $ 1,899,000,000 | $ 1,932,000,000 |