If the return on equity is too good to be true, then it probably is
Let us delve further in the numbers. On page 87 of the annual report, management explained that it acquired 19,185,828 common stock in 2017. But certainly the average cost could not be $1,047 - which can be calculated as the cost of $20.1 billion divided by 19.18 million of common stock - since the stock traded as low as $69 and as high as $77 in 2017. So, to estimate the true average cost, I had to find how many shares the company had acquired to date, and for that, I turned to page 68, where management reported on the book value figures.