The advertisement from Capital One had many of the same promises that other banks offer for high-yield savings accounts: There were no fees, no minimum deposits and the money would earn much more in interest than in traditional bank accounts. “What’s the catch? There is none,” the bank boasted. But, according to a lawsuit filed against Capital One on Tuesday by the Consumer Financial Protection Bureau, there was one, and it cost depositors more than $2 billion. For years, Capital One held interests artificially low in the high-yield product, to 0.30% annually last summer, for instance, even as the Federal Reserve raised rates above 5%. Banks are generally permitted to pay as little in interest as their customers will permit, but Capital One went too far, according to the lawsuit, by deliberately confusing its customers about its products.