GMAC, the financial services group owned by Cerberus Capital Management and General Motors, is considering the sale of at least part of ResCap, its troubled mortgage lender, the Financial Times reported.Robert Hull, chief financial officer, said on Tuesday that while ResCap remained an integral part of GMAC's business, the parent company was "looking at all options". Negotiations are already under way. He declined to give further details.GMAC reported a total loss in 2007 of US$2.3 billion, compared with a US$2.1bn profit the previous year. Losses on car loans, the firm's traditional business, is "relatively mild" and in line with previous economic downturns.However mortgage losses, as with scores of prominent lenders in the mortgage chain in the US, is much more bleak.Any review of the mortgage business of GMAC may eventually have repercussions for the firm's mortgage funding business in Australia, GMAC-RFC, which is one of the few lenders to specialise in the Australian variant on sub-prime lending, though GMAC is a minnow in even that niche.