Moody's cut Time Warner's ( TWX) senior unsecured debt rating one notch, citing its increased leverage as the media giant expands its stock buyback. The New York bond rating firm cut its rating to Baa2, its second-lowest investment grade level, from Baa1. The outlook is stable. The news comes on the heels of Time Warner's agreement last month to boost its stock buyback to $20 billion from the earlier $12.5 billion, under a truce with activist shareholder Carl Icahn. Icahn had been seeking to remove management but failed to gain traction with Wall Street and gave up. On Monday, Time Warner fell 19 cents to $17.24.