"MM" -- Why double Ms??

I have seen a financial state document indicating

"$950MM."

I know MM means "x1 million" or adding 6 zeros.
Can anyone explain why M is DOUBLED??

For instance, in the case "x 1 thousand" or adding 3 zeros, we onlyd add one K: such as "$950K" (= 950 thousand dollars.)

I don't know. I'd only put one "M". Maybe they're thinking in Latin.

The abbreviation M is the the Roman Numeral for 1000, thus MM has been adopted to mean 1000 x 1000 which would be 1 million. The proper Roman numeration of the term MM would be 2000 however.

A lot of times abbreviations are doubled to show that something is plural. For example, p. can mean page ("cited on p. 17") but pp. means pages ("read pp. 85-103"). Perhaps that's what's going on here with your M.