Expression: "spill my guts" US slang?

Hi, I understand that the expression to spill one’s guts on/about something means to ramble about something. I wonder why I can’t find a decent definition of this phrase in any of the online dictionaries except the Urban one. So, would you classify the phrase as “American slang”?[YSaerTTEW443543]

TOEIC listening, photographs: At the optician’s[YSaerTTEW443543]

As slang certainly, and rather rude slang at that. In my experience, it does not mean to ramble, which is too laid back an activity. To spill one’s guts (to me) is to tell everything, and usually in some sort of confession, forced or voluntary.

Here is Wiktionary’s effort:

[i]spill one’s guts

  1. (slang) (idiomatic) To confess, or to divulge secrets, typically speaking freely and at length after a change of motive or an incentive.

At first, the suspect would not tell us anything about the other participants in the crime. But after being offered a deal, he spilled his guts.

And here is a BrE definition:

Vrb phrs. 1. To confess or reveal the truth.
2. To vomit. Probably a misuse of version 1 due to its similarity with ‘spew one’s guts up’.

And an AmE / OzE one:

spill one’s guts v. Confess all.