where is safari auto generated passwords saved?

where is safari auto generated passwords saved?

They're saved with all the other passwords saved in Safari. On Mac, they are in Safari menu (top-left of screen, next to apple logo) > Preferences > Passwords > enter your mac passwords to access

and how safe are these passwords. can it be used for online bank account?

These are just randomly generated passwords that are very long and complex. Pratically speaking, they're probably more safe to use than a password you create on your own - definitley safe for use with your bank.

can I have access to these password if I log into my Apple ID on another Mac?

Yup. You'll need to enable iCloud Keychain on both devices and they will stay in sync with each other (though it sounds like you might already have it enabled.)

The passwords should be in Keychain Access, which is an application on the computer. Unless you set up iCloud Keychain syncing on another computer, you won't have access to the passwords on another computer.