You can take that to the bank!
take-it-to-the-bank. Verb. (idiomatic) Said to emphasize that something is known for sure. www.yourdictionary.com
Figurative: "What was said is the absolute truth and can be verified by a third party source." Comes from an obscure reference to cheques (or checks, if you're American), in that such is a guarantee that you can take the document to the bank and redeem it for its face value. Urban Dictionary