It's a custom material (since I'm using UE4) - there's small detail (grass, snow, sand etc) with their own normal maps, and that's all filtered to break up tiling and applied to the terrain.

The other part is the macro-level stuff that you see more of when you're zoomed out. I did the landscape using Quadspinner Gaea to simulate erosion based on a heightmap I drew with the basic shapes I wanted. Gaea lets me do a colour map based on terrain features, which I added on top of the small detail, and an 8K normal map which I blend with the detail normals based on the distance to the camera. The normal map adds a lot of little hills and valleys that are normally invisible since they're only small variations in the height map.