Also 20 million is a very conservative guess of how many Russians the USSR killed, even if you're just talking Stalin alone and you exclude the Holodomor because they starved mostly Ukrainians.
"Medevedev's grim bookkeeping included the following tragic episodes: 1 million imprisoned or exiled between 1927 to 1929; 9 to 11 million peasants forced off their lands and another 2 to 3 million peasants arrested or exiled in the mass collectivization program; 6 to 7 million killed by an artificial famine in 1932-1934; 1 million exiled from Moscow and Leningrad in 1935; 1 million executed during the ''Great Terror'' of 1937-1938; 4 to 6 million dispatched to forced labor camps; 10 to 12 million people forcibly relocated during World War II; and at least 1 million arrested for various “political crimes” from 1946 to 1953.
Indeed, Aleksandr Solzhenitsyn, the literary giant who wrote harrowingly about the Soviet gulag system, claimed the true number of Stalin’s victims might have been as high as 60 million.
Most other estimates from reputed scholars and historians tend to range from between 20 and 60 million.
In his book, “Unnatural Deaths in the U.S.S.R.: 1928-1954,” I.G. Dyadkin estimated that the USSR suffered 56 to 62 million "unnatural deaths" during that period, with 34 to 49 million directly linked to Stalin.
In “Europe A History,” British historian Norman Davies counted 50 million killed between 1924-53, excluding wartime casualties.
Alexander Nikolaevich Yakovlev, a Soviet politician and historian, estimated 35 million deaths.
Even some who have put out estimates based on research admit their calculations may be inadequate.
http://www.ibtimes.com/how-many-people-did-joseph-stalin-kill-1111789