A leap from laggard to champ by the Westpac institutional banking division over the half year to March 2016 has reversed a rare negative in the group's full year result six months ago. A rare blip in this period's result is a dip in the profit of the consumer bank - one of two divisions, along with business, that has been pouring investment into priority, if faddish, measures.The statutory net profit for Westpac over the half was A$3.907 million, up six per cent. Cash earnings were just over $4.0 billion, up three per cent.One motor within Westpac's mortgage colossus is in reverse. The bank put the interest-only component of the mortgage portfolio at 50 per cent and at 46 per cent of flows over the half. But the bank will have to cut new flows of interest-only loans to 30 per cent by later this year or face grief from the banking regulator.In keeping with most of the bank's analytical disclosure around mortgages the numbers for interest-only loans come with a carve out for all lending under the RAMS banner.Peter King, Westpac chief financial officer, said the RAMS brand had around $12 billion in mortgages and explained that the bank managed the relevant data on a separate systemWestpac Institutional Bank, influential core at the bank, rebounded after a rare down year in 2016. WIB produced a return on equity, on a cash basis, of 14.1 per cent for the half, a nose above the group ROE of 14 per cent. The latter is bang on the top of the bank's target range of 13 per cent to 14 per cent, and right in line with the average of large banks.