Virtually everything worked in big banks' favor in the second quarter, but there's no shortage of things that could go wrong. JPMorgan Chase, Bank of America, Citigroup, Wells Fargo and Goldman Sachs all reported second-quarter earnings Tuesday. The results were overwhelmingly positive, although stock-price reactions were mixed. Goldman gained 9% on surging investment-banking fees and trading revenue. Citigroup dropped 5%, after management implied that returns in the second half wouldn't be as strong. The others had less dramatic moves. Morgan Stanley reports results Wednesday.

All five banks topped earnings and revenue estimates. Each showed improved efficiency overall, with operating expenses declining as a percentage of revenue. Credit losses remained subdued. Some numbers were cartoonishly good. JPMorgan's annualized return on equity was 24%, when analysts were forecasting 19%. It got help from investment gains on its shares in Visa. Goldman, too, reported a 24% return on equity.

JPMorgan Chief Executive Jamie Dimon said, "It's getting close to as good as it gets. We just don't know how long it's going to last." Jeremy Barnum, JPMorgan's chief financial officer, said "the market is clearly extremely risk-on, and we're kind of takers of that."