The phrase "ideal complement" means a perfect match or combination that goes well together. It refers to two things or people that are the best fit for each other and enhance each other's qualities. Full definition
The Fund is an ideal complement to bullion for investors interested in silver; exposure to both equities and bullion can provide better risk - adjusted returns over the long - term; (ninepoint.com)
The «more than» is decisive, for the evils God receives are like impulses that God then renders into a richness of contrast, supplementing evil with its ideal complement, and so achieving aesthetic harmony. (religion-online.org)
Ely's second basic objection to Whitehead's God centers around God's complementary function whereby actual evils are confronted with their «ideal complements» and actual values are enhanced by their complements. (religion-online.org)