It was harshest on horses, then on the soldiers, then the officers. The Marshals and Napoleon and his guard suffered the least.

Leaving Moscow, there were 90,000 infantry, 15,000 cavalry, 569 cannon and 10,000 wagons. They took with them wagons full of Chinese silk, sables, gold ingots, suits of armor and even a prince's jewel encrusted spittoon.

The entire way out of Russia they were harassed by cossacks(who almost captured the Emperor), and if they escaped the terrible fate of being captured by one, they were likely to die of starvation or exposure.

At times Napoleon himself marched with his men, but both he and many of his men were southerners and they suffered bitterly from the cold. While most of them had ample protection from the cold, their faces were not covered and this caused their lips to crack, frost bite on their nose and in some cases, permanent blindness.

Some French soldiers were lured by Russian peasants into their homes with promises of brandy and food, only to be brutally murdered, sometimes in their sleep by having their throats slit. There is one instance where an English observer who accompanied Kutusov saw sixty French soldiers, naked, who had their necks laid upon a felled tree as Russian men and women with large sticks, repeatedly struck the French in their heads to 'blow out their brains.'

As the cold worsened, some men would take refuge inside horses who had been disemboweled for warmth. When a soldier fell, his brothers would strip him of boots and any food and left him unburied.

Arriving in Vilna past the Russian frontier would arrive 40-50,000 men, with a negligible number of horses.

What is often not represented during this campaign is that the Russians suffered just as the Grand Armee did. Leaving Tarutino with 110,000 men, only 40,000 would arrive in Vilna.

Both sides suffered a very large percentage of casualties at the Battle of the Berezina. Three armies converged on the retreating French, close to the frontier of Russia, just as they were trying to cross a river. However this river had thawed out of season, and there was one Russian army across the river, with two on the same side as the French. Kutusov had no the bravery to face Napoleon again and kept his third army away as the French fought across the river, building a bridge under fire, and defeated the advances of both Russian armies.

Many French stragglers refused to cross the bridge and were left behind, though they were given ample warning and time to do so. Perhaps 10-20,000 were left at this juncture.

Sources - Clausewitz, The Campaign of 1812 in Russia

Cronin - Napoleon Bonaparte, An Intimate Biography