A windfall tax break and a higher-than-expected profit forecast did little to protect Macquarie Group from the ravages of the ASX market rout on Tuesday.The share price of the country's largest investment bank shed 5.3 per cent to close at A$97.88, making it the worst performer among listed banks.However, the dumping of the company's stock came after managing director Nicholas Moore upgraded earnings guidance, signalling that Macquarie was in line to increase full year profit by 10 per cent on the 2017 result of $2.2 billion."Trading conditions across the Group were satisfactory in the December 2017 quarter," he said."Macquarie remains well positioned to deliver superior performance in the medium-term due to our deep expertise in major markets, strength in diversity and ability to adapt the portfolio mix to changing market conditions."Moore said he expected the 2018 result to benefit from cost reduction programs and a "proven risk management framework and culture".Macquarie's share price has surged since September last year after investors began to account for the benefits of the corporate income tax cuts it will enjoy on its US earnings next year.The US tax reforms, approved by Congress late last year, are expected to add around A$80 million to the group's bottom line in 2019.Earnings momentum in the group is continuing to be driven by the Macquarie Capital division, which completed 107 corporate transactions during the December quarter collectively worth $35 billion.Most of that activity was driven by deal making in the infrastructure and energy sectors in Europe and North America.Moore painted a less bullish picture of growth in the company's banking and financial services division, indicating that deposit growth had been flat in the quarter.He said Macquarie had grown its mortgage book by four per cent in the three months to the end of December.