Facebook Inc. FB, +0.20% has asked big U.S. banks to share financial information on their customers that includes checking account balances and card transactions, as it seeks to expand its own service offer and stem slowing growth, The Wall Street Journal reported on Monday. Citing people familiar with the matter, the paper said Facebook is aiming to become a platform where people buy and sell goods and services, and has asked JPMorgan Chase & Co. JPM, -0.08% , Wells Fargo & Co. WFC, +2.14% , Citigroup Inc. C, +0.81% and U.S. Bancorp USB, +0.66% to discuss ways it could serve bank customers on Facebook Messenger. The social-media giant has pitched a feature that would display current account balances, as well as fraud alerts. The sticking point is data privacy and one bank has already pulled back, said the paper. Facebook stock lost 20% of its value, equal to about $120 billion in market cap, in one day after its recent earnings report that included the news that growth is starting to slow. Shares were up 1.8% Monday, and have gained 2.6% in 2018, while the S&P 500 SPX, +0.29% has gained 6%.