Bitcoin already has a toehold in mainstream finance. : At first, bitcoin was a way to make payments without banks. Now, with more than $100 billion (Dh367 billion) stashed in digital currencies, banks are debating whether and how to get in on the action.Goldman Sachs Group Inc. Chief Executive Officer Lloyd Blankfein tweeted on Tuesday that his firm is examining the cryptocurrency. Other global investment banks are looking into facilitating trades of bitcoin and other cryptocurrencies, according to industry consultants.