A federal judge on Tuesday formally declared Detroit bankrupt, a landmark ruling that clears the way for potentially sweeping cuts to city worker pensions and retirement benefits and for steep and possibly precedent-setting losses to the cash-strapped city’s bond holders. The ruling by U.S. Judge Steven Rhodes, who cited the city’s dismal finances and $18 billion owed to a multitude of creditors in support of his decision, marks a watershed in the history of Detroit. Once known as the cradle of the U.S. auto industry, the arsenal of democracy and the birthplace of Motown music, Detroit now adds an ignominious new title: largest bankrupt city in U.S. history.