Repricing of Commonwealth Bank's investment lending book late last year is helping to insulate the bank from elevated funding costs in wholesale markets, with the bank reporting a stable net interest margin for the half year to December 2015.Bank management presented a largely sanguine attitude to the widening of spreads on bank funding costs rattling global credit markets of late.CBA's net interest margin was flat on the June 2015 half at 2.06 per cent, but down five basis points on the December 2014 half.David Craig, the bank's chief financial officer, told an investor briefing yesterday, in connection with credit market upheavals, that "we do not see trends that are impacting us."We remain pre-funded. We have done a substantial percentage of our funding this year," he said.CBA treasurer Paolo Tonucci said the "impact of wholesale funding costs has been modest," an observation that may take into account the overall decline in bond yields as capital markets recalibrate in the face of collapsing equity values."If it continues, it will have an impact," Tonucci said."In terms of basis spread, which has seen some media attention, that comes through a bit quicker."CBA chief executive Ian Narev attempted to position the most recent capital markets shocks as unexceptional."In these sorts of markets, there's a tendency to say this happened over the last four weeks, what happens if it continues for the next six months."While concern among investment analysts over funding costs was one theme of yesterday's profit presentation by CBA, anxiety over the level of growth in the institutional and markets business also peppered the Q&A."Our returns in the institutional and markets business are not as high as in other parts of the sector," Narev explained."As long as we grow in a good, risk adjusted way we do have the appetite to grow it."I can't imagine that in the near term it will reshape the [group's] business and it's not intended to."