You'll find the details of the insurance coverage during the car booking process. The coverages provided are generally inclusive of collision Insurance, burglary Insurance etc., which are provided by the car rental company.
Once you completed the booking, you'll also find the insurance details in the rental agreement you'll sign when you pick up the car.
Currently, the Travel+ program does not offer an option to increase insurance coverage. But, you may still place the request with car rental company directly when picking up your car. The additional fee for added insurance is charged by each car rental company.
Gentle reminder: Any unauthorized cross-border activities will invalidate the insurance.