In United Services Automobile Ass'n v. Empire Fire & Marine Insurance Co., 134 Ariz. 64, 653 P.2d 712 (App. 1982), the driver, Richards, was driving a non-owned vehicle. The vehicle was insured under a primary policy with Security Mutual and an umbrella policy with Empire. Richards had his own primary coverage with USAA. Security Mutual paid its policy limits, but a dispute arose as to how remaining damages should be paid. Although the USAA policy had a clause making it excess insurance because Richards was driving someone else's automobile, this court observed that the USAA policy "necessarily contemplated a different and probably a greater risk than that covered by the Empire policy." Id. at 66, 653 P.2d at 714. In refusing USAA's request to prorate the remaining loss between the two policies, this court found that the USAA policy should pay ahead of Empire's umbrella policy. The Court reasoned that "there is certainty and simplicity in a rule which holds insurers who issue residual protection only are last to pay so long as that is their expressed intent." Id.