Arnob:

The IDP (international driving permit) is really nothing more than a translation of the text of your driving licence into a variety of languages, English being one of them. If your present (national) driving licence is already printed in the English language, then the IDP really isn't much use to you - in fact, most North American rental agencies and police would probably not even know what it is. having said that, though, it's probably best to get an IDP "just in case" - they are usually not expensive.

As for renting, if you rent any motor vehicle (car, motorcycle, truck) from an established rental company (as opposed to renting it from a friend or acquaintence), you can pretty much take for granted that the vehicle will have liability insurance sufficient to cover the minimum required for all 50 states and Canada. The North American rental companies rarely, if ever, provide theft, collision damage, or other 'extended' insurance coverage as basic - you have to pay extra for this if you want it, and the daily charges for the extra insurance coverages can be very high - best to do your homework and find out exactly what they are ahead of time.

But, the basic gist is this: If you rent a vehicle in North America, it will come with the legally required basic, minimum liability insurance. That much you can take for granted - I think it is against the law to rent a vehicle that is not insured for liability.