As others said - NOT normal. When the lever is in "P", the car may rock a few inches, until the dog in the box is engaged, but should then hold.
But please do NOT use the "P" function as the primary source of holding a car when stationary - on any kind of automatic gearbox. Why? Well which are cheaper to repair/replace - handbrake cables or gearboxes?

If parking on a hill with just the "P" fuction and no handbrake, then you put massive strain on both the selector mechanism, and the internals of the gearbox.
This is part of the gearbox internal which uses the "P" function - it is the second from the bottom - square "dogs" one up from the helical final drive gear. Oh, and RedRobin should know exactly what that is!

