As I only drink almond milk, I had to look that up and found this for you.
This actually depends on the breed of cow as well as its age and the time of year. Certain breeds, like Guernsey Cattle, are noted for producing highbutterfat milk and are formed into dairy herds for exactly that reason. Others, like Angus, are better at beef production and are rarely found among dairy herds.
As cows age, their milk contains less butterfat. Too, during the summer, when cows normally have access to green forage, their milk is higher in fat.
But -- on average, across breeds, ages, and seasons -- whole milk contains in the area of 3.5%-4.5% butterfat. In some places, with some cows, at some times, that might rise as high as 6% or even a bit higher.