In this instance, the entire amount of sales proceeds is taxable because if you read the explanation on the Brighthouse Financial 1099-B, the number of MetLife shares that you own did not change. Therefore, you received "free" shares of Brighthouse Financial stock and "free" fractional shares that were paid out to you in cash. The cost basis of the fractional shares is zero and should be reported as such on Form 8949. My gut tells me that this is a short-term capital gain, but I'm not 100% sure on this.
