Commonwealth Bank will buy back four-fifths of its government guaranteed debt, following a tender by investors conducted last week.CBA said it will buy back A$3.1 billion of the floating-rate notes and $736 million of the fixed-rate notes that mature in 2013 and 2014. The bank will still have $1.4 billion in debt that carries the Australian government guarantee.Local and foreign banks had $68.3 billion of wholesale liabilities still guaranteed by the Australian government at the end of December 2012, according to Treasury.