You will likely need to call to find out the fare rules.

Even if it's nonrefundable, you will have the full value to apply to travel for a year from the original flight date. UA will charge you a separate change fee at the time you use it to book new travel (the amount depending on the old ticket's fare rules, but typically $200 for domestic and $300 for international). If there is still any value left over, they will issue it to you as an electronic travel certificate at that time.

I just booked a refundable W fare recently. I was frankly surprised about that, but the agent checked the rules (as I was using a non-refundable P fare's residual credit, in fact, to pay for it).