The National Security Archive has posted a newly declassified document, a 1956 Air Force nuclear targeting plan setting requirements to be fulfilled by 1959. It lists over 1100 airfields and 1200 cities in the Soviet Union and allied states that were marked for destruction. The targeting also planned attacks on "population" as well as military installations.
I haven't studied the huge document, but I have some initial impressions. The targeting plan reflects the mindset of General Curtis LeMay and the Strategic Air Command during the 1950s: they wanted to make the USSR "a smoking radiating ruin at the end of two hours" and were willing to strike first. They showed no hesitation about hitting purely civilian targets. The 1956 plan was also probably part of SAC's campaign to increase the Air Force bomber budget, which was being threatened by the acceleration of programs for long range ballistic missiles.
It was precisely this plan for mindless destruction that appalled Defense Secretary Robert McNamara when he saw the first SIOP [Single Integrated Operational Plan] developed by SAC at the end of the Eisenhower Administration. He persuaded President Kennedy to develop options in the nuclear war plan, including withholds of civilian targets and "counterforce" against military ones.
As horrible as any nuclear exchange would be, there were and are ways to make it somewhat less horrible.