This is completely normal and expected. Happens in April (small) and December (big un) each year. Look at the fund's fees and distributions tab for any fund you hold and it should tell you the last several years' worth of dividend/cap gains distribution percentages and the dates.
They are dropping the individual share price and then buying back in to it, so the price will end up being the same more or less once the dust settles. Just don't panic and think this is some horrible glitch... ;)
If you have dividends/cap gains set to automatically reinvest, they'll repurchase (reinvest) on Monday, at the new lower price per. If you don't, then you'll have cash sitting in your account as of the settlement date (so end of day Monday december 16th). Basic account worth/$ will be the same tho.
And for what it's worth, they always announce this stuff early. They have a banner at the top of the webpage:
https://www.fidelity.com/mutual-funds/information/distributions#/?table=actualsIt's not totally accurate as far as the percentages at this time (updated throughout the month), but it can tell you the sell date/settlement date.
Also expect a possible hail mary short term cap gain distribution the last day or two before the end of the year. Doesn't always happen, but is possible.
Not important for anything held inside a tax deferred account, but if you have dividends/cap gains generated in a taxable investment account, you'll need to prepare for that as taxable income generated even if you reinvested it all, and plan accordingly.