Credit losses in Commonwealth Bank's Institutional Banking and Markets division spiked over the December 2017 half year, amid a further overall improvement in group credit quality for the bank.The loan impairment expense for the group "decreased one per cent on the December 2016 half to A$596 million," the bank said.Annualised as a percentage of average gross loans and acceptances, the bad debt charge decreased one basis point to 16 basis points. In Institutional, the bad debt charge for the current half was $105 million, a five-fold increase on an unusually low expense in the June 2017 half and more than double the expense in the December 2016 half.In keeping with trends from recent years, CBA is winding back its risk appetite in Institutional."Institutional banking is getting smaller. We're committed to it, but it's getting smaller," Ian Narev, CBA's chief executive officer told an investor briefing yesterday.