National Australia Bank's 2017/18 first half earnings result was flat overall, but included notable peaks and troughs.The strongest performance came in from NAB's business and private banking division which yielded A$1.48 billion for the half, up 8.3 per cent on the comparable period last year.NAB's consumer banking and wealth division also performed well, returning an $804 million profit, up 5.2 per cent on the first half of 2018. Higher margins and growth in housing lending, in line with system, combined with lower credit impairment charges, made for a good half.Corporate and institutional banking returned $778 million profit down 1.6 per cent against the comparable period last year, on the back of softer markets related income and the sale of the private wealth business in Asia.NAB's New Zealand banking division performed solidly with $494 million profit, an 8.6 per cent improvement on the comparable period last year. Again, this was a result largely on the back of good performance in the Auckland housing and SME sectors.On the downside, expenses were up 25.3 per cent, or 5.4 per cent if restructuring related costs are excluded.Key ratios as at 31 March 2018 group common equity tier 1 (CET1) ratio of 10.21 per cent, up 15 basis points from the last half NAB expects to meet Apra's "unquestionably strong" target of 10.5 per cent "in an orderly manner" by January 2020 leverage ratio - calculated on an "APRA basis" - of 5.6 per cent liquidity coverage ratio (quarterly average) of 127 per cent net stable funding ratio of 115 per cent