With that said, since the OP specified a total WAllied victory scenario, presumably by driving the USSR to collapse after a protracted and bloody war, I'll focus on that for the rest of this post. The place to look to gain some indication of American peace intentions would be US planning for war in this period.
The first American war plans of this era, the 1946 Pincher-series, didn't contain anything in the way of political objectives in the event of victory as that plan was almost entirely focused on the first 18 months of hostilies, with only vague thoughts given to the later stages of such a war and none at all for the final outcome. The 1947-48 Broiler-series of plans was the first to address any sort of end-state settlement and envisioned that, in the event of total victory, the peace settlement would involve the retention of a unitary Russian state within the 1939 borders and the disarmament of said state, but was a bit vague on further details largely because the planners lacked any political guidance...
-American War Plans 1945-1950, Steven T Ross, Pg 62.
The above political assumptions were largely retained in the subsequent 1948-49 Bushwhacker-Halfmoon series (although Bushwhacker at one point rather bizarrely denied the idea of forcing unconditional surrender, despite the fact that it is difficult to see how else such political objectives could be achieved). It wasn't until the 1949 Offtackle-series of warplans that the planners received any sort of political guidance to alter and refine their thinking for a political settlement in the event of total victory. This plan did call for the break-up of the USSR, but a core Russian state would be allowed to exist so presumably the division would be done along the lines of making the 16 Soviet republics independent. While a communist regime might be permitted to exist within the territory of the RSFSR, it would do so in a disarmed and peaceable state. Plans after the Offtackle-series (such as the famous Dropshot-series) largely stuck to these ideals.
-American War Plans 1945-1950, Steven T Ross, Pg 111-112.
Of course whether that final requirement could be fulfilled during and in the aftermath of a WW3 scenario is... debatable.