Transocean Deepwater Inc. will pay the second-largest environmental fine in U.S. history for its role in the deadly 2010 Deepwater Horizon explosion and spill in the Gulf of Mexico, the Justice Department said Thursday. The company was sentenced to pay $400 million and other penalties after it pleaded guilty in a Louisiana federal court Thursday to violating the Clean Water Act by its illegal conduct leading to the disaster, Attorney General Eric Holder said.