National Australia Bank is talking to global custody providers about options for its custody business, NAB Asset Servicing. The bank announced yesterday that was holding discussions with a number of parties.NAB Asset Servicing is the biggest player in the domestic custody market. According to the Australian Custodial Services Association, at the end of last year NAS had A$632 billion of assets under custody.NAS increased its assets under custody by 11.4 per cent over the six months to December, compared with average growth of 8.3 per cent for the sector over the same period.Other leading custodians include JP Morgan, with $419 billion of assets under custody at the end of last year, BNP Paribas ($305 billion of assets), Citigroup, ($254 billion of assets) and State Street ($199 billion of assets).The sector's $2.3 trillion of assets under custody is made up of $1.7 trillion of Australian assets and $650 billion of non-Australian assets held for Australian investors. In addition, custodians held $959 million of Australian assets for foreign investors.While NAB is strong in the local market, custody is increasingly a global business.NAB said in its statement that it currently offered global as well as local custody services.However, yesterday's announcement suggests it is looking for a new global partner or is considering a sale of the business.ANZ sold its custody business to JP Morgan in 2009.