And yes, it is a kind of passive voice. Normally, Russian academic grammar school does not call it "passive voice" since there is no passive verb in it. It calls it "неопределенно-личное предложение" as it-ogo wrote. But this structure is a functional equivalent of the passive voice. It is used to "remove" the real subject from the phrase since we do not know its name. "нас не задержат" = "we will not be detained". Although grammatically it is structured differently.