A: There’s a new Italian restaurant across the street. How about trying it out for lunch?

B: Sure, but let me foot the bill today. You paid for dinner last time.

Note: This idiom simply means “to sign your name at the foot or bottom of the bill.” Obviously the one who “foots the bill” assumes the responsibility for paying it. For example: Don’t be angry, I will foot the bill for the damages to your car.