Federal authorities are expected to arrest Sheldon Silver, the powerful speaker of the New York State Assembly, on corruption charges on Thursday, people with knowledge of the matter said, in a case that is likely to throw Albany into disarray. The investigation that led to the expected charges against Mr. Silver, a Democrat from the Lower East Side of Manhattan who has served as speaker for more than two decades, began after Gov. Andrew M. Cuomo in March abruptly shut down an anticorruption commission he had created in 2013. Details of the specific charges to be brought against Mr. Silver...