(Adds details from settlements, Credit Suisse comment, background, byline)
By Jonathan Stempel
NEW YORK, Sept 28 (Reuters) - Credit Suisse Group AG was fined $10 million on Friday by the U.S. Securities and Exchange Commission and New York Attorney General Barbara Underwood over its handling of retail customer orders, including through its dark pool.
Both regulators said the Swiss bank's Retail Execution Services business, which closed in 2015, treated orders for which execution quality was not required to be publicly reported less favorably than orders subject to such reporting.
They also said Credit Suisse promised ordinary customers access to broad liquidity in dark pools, including its own, but processed only a "minimal" number of "held orders," which must be executed immediately at market prices, in that manner.
"Wall Street firms cannot offer misleading assurances about the execution quality they provide their customers while engaging in electronic trading strategies that undermine those promises," Underwood said in a statement.
Dark pools are private trading venues that let people trade quietly, often in large orders with minimal price movement.
Credit Suisse's settlement covers alleged improper treatment of customer orders from mid-2011 through March 2015.
The bank is paying $5 million each to the SEC and Underwood's office, without admitting or denying wrongdoing.
Credit Suisse spokeswoman Nicole Sharp said the bank was pleased to settle.
New York has been investigating electronic and high-frequency trading practices on Wall Street for several years.
Underwood, who became the state's attorney general after her predecessor, Eric Schneiderman, resigned in May, said her office has recouped $130.5 million of penalties from four banks in connection with the investigations. (Reporting by Jonathan Stempel in New York; editing by Jonathan Oatis)