Moscow is not warmer than Detroit. It is significantly colder, moreso in the summer but winters are colder too. The mean daily maximum in January is only 25.0F, which is less than the mean daily mean [average of max & min] for Detroit (25.8F), with the daily mean being 5F colder (20.8F). For the year, it's way colder. The normal annual mean is 3.6F colder than even Minneapolis. A normal year in Moscow (43.3F) is 0.7F colder than the coldest year ever recorded in Detroit (44.0F, in 1875).
The difference is greatest in the late summer. The normal August in Moscow is 2.2F colder than the record coldest August in Detroit (65.9F, 1915) and the normal September is a full 4F coldest than the record coldest in Detroit (57.4F, in 1918).