Sue for an armistice restoring the 1939 boundaries in the West while you still hold the advantage in Europe. The world has already suffered enough. No-one will win this war.
That would actually fit the requirements of both sides for an armistice. Norway gets its democratic government back, Sweden stays fascist... France, Netherlands, Belgium restored, Italy neutralized. Eastern Europe remains under the German iron fisted tyranny. Norway, northern France, Netherlands become UK's strategic missile and bomber defence, and US' economic colonies. Allies demolish everything of value in those parts of Germany they still hold, and deport as many civilians as they can get their hands on in the two weeks it would take them to withdraw behind 1939 borders. (Their towns and villages are torched and the fields salted, all records are destroyed, so those people count as casualties of war for all intents and purposes. Somewhere in central Algeria or in the nuclear scorched wastelands between Cape Cod and the Hudson river, in the abandoned English midlands or in the deserts of western Australia, they wil serve the rest of their lives as labor battalions, the survivors given homesteads after twenty years of servitude.)
Germany calls its fleets back into port and ceases assistance to the South American axis, leaving them to their eventual dismemberment by US and allied forces. Soviet Union loses India, continues to duke it out with the Allies over the worthless sands of inner Mongolia and the Hindukush, eventually also agrees to cease-fire after it realizes Germany is shifting its 99 armored divisions east and is going to let 99 red balloons fly on short notice. Eventually they agree to become a client of the US but stay communist for internal propaganda purposes. US strong-arms Mexico and other unaligned nations into rendering massive assistance to the northern American reconstruction effort. (Labor battalions in blue overalls with Geiger counters for cleaning up the radiating mess in the northeast US, also shipments of cereals and other food stuffs.) Germany turns to a policy of austerity and forced resettlement in its eastern territories (which are out of range of the Allied medium range strategic bombers).
The world slowly recovers, by 1980 private automobiles start to become common again outside the US, by 2000 electronic computers are available on the free market. Small scale proxy wars continue in the middle east but neither side escalates things out of fear of triggering another nuclear armageddon. Eventually someone discovers nuclear fusion and the internet, and extends humanity's probation time to the 21st century. Until the next nuclear war.