First of all, it is very difficult to imagine that the United States would have ever chosen not to help the Western European countries after WWII. The US was simply too suspicious of the Soviets to allow this to happen. Therefore, the most likely outcome would have been that the US would have given some other kinds of aid and things would have turned out essentially the same as they did in real life.
If we are going to assume, though, that the US gave no aid whatsoever to Europe, it is still hard to know what would have happened. The US and the other Allies still controlled Western Germany. This makes it very unlikely that the Soviets could have tried to invade. However, they might well have taken some countries on the periphery of Europe such as Greece. The heart of Western Europe would likely have been much poorer and socialist and or communist parties might have had more power even as those countries remained democratic.