Shareholders' Equity (Schedule of Share Repurchases) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
Jan. 31, 2019	Jan. 31, 2018	Jan. 31, 2017
Share Repurchases [Abstract]
Total number of shares repurchased	79.5	104.9	119.9
Average price paid per share	$ 93.18	$ 79.11	$ 69.18
Total amount paid for share repurchases	$ 7,410	$ 8,296	$ 8,298

Equity impact of the cost of common and preferred stock that were repurchased during the period. Recorded using the cost method.

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