NEW YORK--(BUSINESS WIRE)--Fitch Ratings has affirmed United States Steel Corporation's (U.S. Steel; NYSE: X) Issuer Default Rating (IDR) and debt ratings at 'BB-'. A full list of rating actions follows at the end of this release. The Rating Outlook is Stable. KEY RATING DRIVERS The ratings reflect U.S. Steel's leading market positions in flat-rolled and tubular steel in the U.S., together with its high degree of control over its raw materials offset by the high fixed costs of integrated steel