Historical Rules · 15 February 2021
Rule 120.10
Official source text from the 15 February 2021 Rules release
Some triggered abilities check whether a permanent has been dealt excess damage. These abilities check after the permanent has been dealt damage by one or more sources. If those sources together dealt an amount of damage to a creature greater than lethal damage, excess damage equal to the difference was dealt to that creature. If those sources together dealt an amount of damage to a planeswalker greater than that planeswalker’s loyalty before the damage was dealt, excess damage equal to the difference was dealt to that planeswalker. If a permanent is both a creature and a planeswalker, the excess damage dealt to that permanent is the greater of those two amounts.