The Globe and Mail reports in its Wednesday edition that with their mortgage books largely insured, the Big Six banks are not likely to endure much pain in a property downturn. The Globe's Tim Kiladze writes that argument could come back to haunt the banks now that the federal government is studying whether mortgage lenders should share in the housing risk. As it stands, Ottawa backstops roughly 60 per cent of the $1.3-trillion mortgage market, and that puts taxpayers -- not the banks -- on the line if it all falls apart. Because homeowners pay for insurance out of their own pockets, and because insurers cover any losses from defaults, the banks are not required to hold capital as a safety cushion against the insured portions of their mortgage books. The idea is to shift the risk away from the economy and taxpayer to the banks. Since 2005, Royal Bank of Canada has nearly tripled the size of its residential mortgage portfolio to $214-billion -- and Ottawa has taken most of the added risk. Accepting risk-sharing has been difficult for some lenders, which have met with the feds and happily laid out some options to curb the country's housing excesses which do not involve increasing capital requirements.