It should because most comforters have larger dimensions than their corresponding mattress size. A king size comforter may be 100 to 110 inches wide and 86 to 88 inches long, which should be enough to cover a California king size mattress’s dimensions.
A king size comforter may hang a bit short off the foot of the mattress or a bit long off the sides. However, the comforter should be big enough to keep sleepers on a California king mattress warm. If you have a thick mattress, you might want to try an oversized king comforter.