JPMorgan's soaring profit was boosted by a one-time $4.6 billion gain on the stake it holds in Visa. That's a big reason the profit blew by analyst estimates.

History lesson: The banks created Visa and many of them still hold legacy stakes. JPMorgan this spring swapped some of its shares in Visa for a different class, leading to a markup on its books.

Results also included a one-off $1 billion gain from unspecified other equity investments.